Trained immunity: a double-edged sword

My last blog post explained that trained immunity, or innate immune memory, provides non-specific protection from secondary infections. The induction of cellular reprogramming in innate immune cells confers an innate immunity with memory characteristics. So far, the only trigger of innate immune memory that we have discussed is microbial triggering, such as triggering from a live attenuated vaccine. But actually the same mechanism of recognition and memory function can also recognize other substances which are not pathogens. In other words, the memory characteristic of the innate immunity mechanism can also be induced by exogenous and endogenous stimuli which are not pathogenic. The fact that trained innate immunity evolved this way, however, does result in harmful effects. Let us have a look at the most recent review paper jointly written by Prof Mihai Netea, who discovered the trained immunity, and the other experts in the field.¹

Netea et al suggested that the reprogramming of the innate immunity and the concomitant increased inflammatory responses to exogenous or endogenous stimuli may have harmful consequences. The induction of trained innate immunity can turn a transient inflammation into a long-lasting effect. Prolonged inflammation is associated with several inflammatory diseases, such as atherosclerosis, and neurodegenerative diseases such as Alzheimer's and dementia, and can also lead to tumour growth and metastasis. The review paper provides evidence from research studies for the association between the innate immunity and the above-mentioned diseases.

Atherosclerosis
Atherosclerosis can lead to heart attack and stroke. Persistent inflammation of vessel wall is characteristic of atherosclerosis. Foam cells, which derived from macrophage*, form a plaque which plays a central role in inflammation during all phases of the atherosclerosis.

A study from Prof Netea found that when *monocytes, an innate immune cell, are stimulated by various micro-organisms, they can develop into *macrophages with persistent ability to promote inflammation, to produce cytokine production and form into foam cells which could lead to atherosclerosis. The stimulated monocytes in the experiment were found to have change at the DNA chromatin level, an indication of the trained immunity process.² The above study indicates that trained immunity stimulated by infections can lead to atherosclerosis.

Alzheimer's disease
Alzheimer's disease is a type of dementia caused by the degeneration of brain cells that process, store and retrieve information, to the point of a loss of function. The disease is characterized by plaques composed of a neurotoxin called β-amyloid. It is hypothesised that the aggregation of the β-amyloid disrupts cell-to-cell communication and activates innate immune cells such as microglia, macrophages which reside in the brain. These immune cells trigger inflammation and ultimately destroy the brain cells.³

In a research study cited by the review, scientists found that peripheral application of inflammatory stimuli in a 3-month old mouse model of Alzheimer's disease, and the second stimulation from β-amyloid plaques at 6-month old leads to a higher β-amyloid plaque load. This indicates a long-lasting training result of microglia.⁴ Moreover, the scientists also found that the functional changes of microglia are accompanied by reprogramming of the cells. This is evidenced by chromatin changes at HIF1α, a gene which usually responds to peripheral trained immunity.^4,5

Cerebral small vessel disease
Cerebral small vessel disease links to systemic inflammation and is a major cause of dementia. According to a research finding cited by the review, in patients with cerebral small vessel disease, peripheral blood-derived monocytes (one type of innate immune cells) have enhanced IL-6 and IL-8 production after **ex vivo stimulation of monocytes with Pam3Cys. Enhanced IL-6 production in the subsequent stimulation is an indication of trained immunity. This shows that the trained immunity contributes to the progression of the disease.⁶ However, a causal link to the pathophysiology of the small vessels in the brain remains to be determined.

Alzheimer's disease and cerebral small vessel disease associated dementia are neurodegenerative diseases occurring generally in older people. In fact, more evidence suggests that there is a link between trained immunity and the inflammatory condition related to an ageing immune system. Therefore, the review suggested that a better understanding of the dark side of trained immunity in ageing populations might help to fight chronic inflammatory diseases such as dementia in elderly patients.

Tumour growth and metastasis
According to the review, chronic inflammation can provide fuels to sustain disease progression and neoplastic transformation, in particular tumour entities. Studies found that trained immunity and the metabolic processes in cancer cells are both reliant on glycolytic metabolism and the up-regulation of the expression and activity of transcription factors such as HIF1α. These findings provide the basis for the interplay between trained immunity and the tumour cells.

Moreover, the review mentioned that innate immune cells infiltrating the tumours' microenvironments can undergo a reprogramming process that leads to the development of maintained inflammatory responses that can boost up the infection-associated proliferation of lymphocytes, impair apoptosis, promote mitochondrial dysfunction and increase oxidative stress. This ultimately promotes the progression of the tumour. Trained cells produce cytokines such as IL-6 and tumour necrosis factor (TNF) that are associated with increased tumorigenicity and the spread of metastases in specific types of tumours. These include oral squamous cell carcinoma and lung, kidney and breast cancer.^7,8

On the other hand, the review mentioned that innate immune cells can be reprogrammed by tumour cells to acquire a more anti-inflammatory situation. This can be exemplified by the low levels of cytokine production in monocytes from chronic lymphocytic leukaemia patients.⁹ Cancer cells also produce a series of soluble mediators that can induce direct epigenetic and metabolic reprogramming in immune cells and can in turn contribute to the progression of the tumour.¹⁰

Conclusion
The reprogramming of the innate immune cells is beneficial when trained immunity results in a fast response to the heterologous pathogen with similar molecular characteristics as the first stimuli. However, from the above examples, we can see that innate immune cells can also be harmful. The resulting prolonged inflammation may also lead to various chronic inflammatory related diseases.



* Monocytes and macrophages are mononuclear cells composing innate immunity. Monocytes are bone-marrow derived leukocytes that circulate in the blood and spleen. Once recruited to tissues, monocytes can differentiate into macrophages and dendritic cells. Macrophages are generally considered terminally-differentiated cells that "engulf" pathogens or toxins and secrete chemokines to recruit other immune cells. The engulfed pathogen is processed by the macrophage and presented to the adaptive immune cells such as B lymphocytes. ** Ex vivo refers to experiments done in cells or tissue from an organism in an external environment with minimal alteration of natural conditions. In the experiment mentioned, the ex vivo stimulation of monocytes were achieved by first isolation of monocytes from blood samples.



References
1. M.G. Netea, J. Dominguez-Andres, L.B. Barreiro, et al. Defining trained immunity and its role in health and disease. Nat. Rev. Immunol., 2020, Jun;20(6): 375-388.
2. J. Leentjens, S. Bekkering, L.A.B. Joosten, et al. Trained innate immunity as a novel mechanism linking infection and the development of atherosclerosis. Circ. Res., 2018,122, 664-669.
3. Beta-amyloid and the amyloid hypothesis. Alzheimer's Association. https://www.alz.org/national/documents/topicsheet_betaamyloid.pdf
4. A.C. Wendeln, K. Degenhardt, L. Kaurani, et al. Innate immune memory in the brain shapes neurological disease hallmarks. Nature, 2018, 556, 332-338.
5. S.C. Cheng, J. Quintin, R.A. Cramer, et al. mTOR- and HIF-1-mediated aerobic glycolysis as metabolic basis for trained immunity. Science, 2014, 345, 1250684-1250684.
6. M.P. Noz, A. tel Telgte, K. Wiegertjes, et al. Trained immunity characteristics are associated with progressive cerebral small vessel disease. Stroke, 2018, 49, 2910-2917.
7. S.H. Lee, H.S. Hong, Z.X. Liu, et al. TNFα enhances cancer stem cell-like phenotype via Notch-Hes1 activation in oral squamous cell carcinoma cells. Biochem. Biophys. Res. Commun., 2012, 424, 58-64.
8. D.R. Hodge, E.M. Hurt, & W.L. Farrar. The role of IL-6 and STAT3 in inflammation and cancer. Eur. J. Cancer, 2005, 41, 2502-2512. 9. T. Jurado-Camino, R. Cordoba, L. Esteban-Burgos, et al. Chronic lymphocytic leukemia: a paradigm of innate immune cross-tolerance. J. Immunol., 2015, 194, 719-727.
10. K. Rabold, M.G. Netea, G.J. Adema, et al. Cellular metabolism of tumor-associated macrophages-functional impact and consequences. FEBS Lett., 2017, 591, 3022-3041.

Coronavirus (19) Should we use a random live attenuated vaccine for COVID-19 prevention?

My last few blog posts discussed non-specific protection effects by live attenuated vaccines. You may be thinking: if live attenuated vaccines have such properties, can we just take any randomly-chosen live attenuated vaccine (e.g. BCG, OPV, or MMR) for COVID-19 prevention? Why should we bother to test these long-existing and widely-used vaccines before we use them as prophylaxis for COVID-19? Well, there are specific characteristics of the innate immunity system that enable the live attenuated vaccines to provide non-specific protection effects. Let us learn about this "trained innate immunity" today.^1,2

Specific protective effect is attained in adaptive immunity level
You may still remember what you learned from secondary school that vaccines are a harmless forms of virus or bacteria (either killed, greatly weakened, or broken down into small parts) that stimulate the production of neutralizing antibodies that can recognize and bind specifically to the surface structure of the pathogen. Once these antibodies are produced, they are maintained at a low level in the body for the rest of the person's life, so that, should the real pathogen invade, the antibodies can recognize it immediately and trigger the concomitant killing process in a very short time. Neutralizing antibodies are a major part of the adaptive immune system and confer the memory characteristic of this immune system. Therefore, the specific protective effect conferred by a vaccine, including the live attenuated vaccine, is achieved via the adaptive immune system.

Non-specific protective effect is initiated via trained innate immunity
Live attenuated vaccines, such as the BCG, OPV, MMR and measles vaccines, however, also exhibit a broader range of protection which can exist for half a year to 5 years. This non-specificity does not involve the specific priming, and so it is not the result of adaptive immunity. Recently, scientists started to realize that vaccines trigger an immune response, which involves a diversity of cells belonging to the innate immune system, to provide a broader range of protection.¹ The cells of the innate immunity may be primed upon encounter with the live attenuated vaccine, acquiring resistance to a second infection against the same pathogen, or unrelated pathogens with similar molecular patterns associated to the target pathogen. This is the basis of the "trained innate immunity". ^1,2,3

The mechanism of how the innate immunity is being trained by live attenuated vaccines and attains a memory characteristic to react against invading pathogens with similar molecular patterns is not yet fully understood. However, as we can see from the evidence mentioned in my previous blog posts, different live attenuated vaccines induced different trained immunity programmes. For example, vaccination with the BCG vaccine can protect animals against secondary infection with Candida albicans and Schistosoma manasoni,4,5 but the other live attenuated vaccines do not have such heterologous protection effects against these pathogens.

Therefore, when we consider making use of the non-specific protection effects of a live attenuated vaccine for preventing COVID-19, it is important to test if the vaccine also works for the disease.

The molecular mechanisms leading to the trained innate immunity
Although the mechanism of how the trained immunity is attained is not fully understood, scientists have found that it involves multiple regulatory layers at the molecular level. This include changes in chromatin organization, transcription of long non-coding RNAs (lncRNAs), DNA methylation, etc. As the change in the chromatin level that alters gene expression is a relatively long-lasting process, this explains how innate immunity cells display a memory function and are thus able to react spontaneously upon the second infection.³

Moreover, recent work has found that haematopoietic stem cells, the progenitor of innate immune cells, also display a memory function. This solves the question of how the innate immune cells such as myeloid cells, with short-lived and an average half-life of 5-7 days, can display a memory function that can be maintained for several months or even years.³

Based on the above findings, we can understand that the heterologous protection against infections induced by live attenuated vaccine is reversible and can last for up to 5 years but is not retained for a whole lifetime.⁶ However, the duration of the protection varies with the vaccine used and with the pathogen that stimulate the non-specific effects. Therefore, it is important also for a clinical trial to find out how long the live attenuated vaccine can provide the non-specific protection against COVID-19, if the vaccine proved to be efficient against the disease.

What are the benefits from knowing more about the nature of trained immunity?
As trained immunity is initiated via the changes in DNA methylation, examination of the DNA's methylation patterns can provide clues to determine whether people are able to undergo trained immunity to stimuli by vaccination of a live attenuated vaccine. The identification of the genes which are differentially methylated in people who respond to the vaccine versus in people who do not respond, could potentially be used as predictors of responsiveness to stimuli that induce trained immunity.⁷



* The references cited is based on the review paper "Defining trained immunity and its role in health and disease" written by M.G. Netea, et al.

References
1. M.G. Netea, L.A.B. Joosten LA, E. Latz, et al. Trained immunity: a program of innate immune memory in health and disease. Science, 2016, 352 (6284): aaf1098.
2. M.G. Netea, J. Quintin, and J.W.M. van der Meer. Trained immunity: a memory for innate host defense. Review. Cell Host Microbe., 2011, May 19;9(5): 355-361.
3. M.G. Netea, J. Dominguez-Andres, L.B. Barreiro, et al. Defining trained immunity and its role in health and disease. Nat. Rev. Immunol., 2020, Jun;20(6): 375-388.
4. J.W. van't Wout, R. Poell, and R. van Furth. The role of BCG/PPD-activated macrophages in resistance against systemic candidiasis in mice. Scand. J. Immunol., 1992, 36, 713-719.
5. J. Tribouley, J. Tribouley-Duret, and M. Appriou. Effect of Bacillus Callmette Guerin (BCG) on the receptivity of nude mice to Schistosoma mansoni. C. R. Seances Soc. Biol. Fil., 1978, 172, 902-904.
6. V. Nankabirwa, J.K. Tumwine, P.M. Mugaba, et al. Child survival and BCG vaccination: a community based prospective cohort study in Uganda. BMC Public Health, 2015, 15, 175.
7. J. Das, D. Verma, M. Gustafsson, et al. Identification of DNA methylation patterns predisposing for an efficient response to BCG vaccination in healthy BCG-naïve subjects. Epigenetics, 2019, 14, 589-601.

Coronavirus (18) Other live attenuated vaccines that may have protective effects against COVID-19

Although only limited evidence has been observed in support of COVID-19 prevention by non-specific effects of the BCG vaccine, this does not exclude the possibility of the vaccine's non-specific preventive effects against COVID-19. On the other hand, there is also a possibility that other live attenuated vaccines could provide non-specific effects against COVID-19 as well, based on the fact that children are subject to vaccine programmes and are less susceptible to COVID-19 infection. This blog post is going to introduce the other three candidate live attenuated vaccines suggested by scientists: oral poliovirus vaccine (OPV), measles vaccine, and MMR (measles, mumps, rubella) vaccine. I would like to share with you the hypothesis on why and how these three vaccines may also provide protection against COVID-19.

Oral poliovirus vaccine (OPV)
OPV is a live attenuated vaccine that helps to prevent the paralysis caused by the poliovirus infection to the central nervous system. In seven randomized controlled trials from 2002 to 2014 in Guinea-Bissau, a country which did not have previous polio infections, the all-cause mortality decreased 19% since a national immunization campaign with OPV was launched.¹ This indicates that OPV has beneficial non-specific effects. In fact, early clinical studies showed that OPV reduced the amount of other viruses that could be isolated from the immunized group of children, when compared with placebo group.^2,3 Most importantly, clinical studies performed from 1969 to 1971 showed that OPV was effective in preventing influenza and the concomitant acute respiratory disease, with a maximum of 3.1-fold morbidity rate reduction.⁴ This indicates that OPV can stimulate the innate immunity* to protect against respiratory infection, thus suggesting that the vaccine may be able to provide temporary protection against COVID-19, a respiratory infection disease.²

Compared to the BCG vaccine, OPV has some important advantages: the BCG vaccine is a weakened bacteria, while poliovirus and coronavirus are both positive-strand RNA viruses. It is likely that poliovirus and coronavirus may induce and be affected by common innate immunity mechanisms.² Therefore OPV is more likely to confer protective effects against COVID-19 than the BCG vaccine.

Moreover, since OPV has a stronger safety record, the risk of complications due to OPV is extremely low. Vaccine-associated paralytic polio develops in 1 per 3 million vaccine doses, mostly in immunocompromised children. On the other hand, up to 1% of BCG vaccine immunized children need medical attention due to some adverse reactions.²

Furthermore, OPV has more than one serotype, so the vaccines could be used sequentially to prolong protection.^2.4 The lower cost, ease of administration, availability, and the ease to scale up production are other advantages. More than a billion doses of OPV are produced and used in over 140 countries per year, while the supply of BCG vaccine is more limited. Therefore a relatively much smaller fraction of OPV should be enough for clinical trials to test its non-specific effects against COVID-19, without needing to fear that its supply to current polio eradication campaigns in developing countries will be limited.² By contrast, the possible use of the BCG vaccine for COVID-19 has already given rise to concerns over the availability of the vaccine as immunotherapy to patients with bladder cancer, due to its limited availability.

Although OPV seems promising in its ability to protect against COVID-19 and many researchers have suggested the testing of the vaccine,² no clinical trial has yet been launched to investigate this. Not even a registration of a relevant trial is seen in any public clinical trials registry platform.

Measles vaccine
According to the World Health Organization, measles is a highly contagious and deadly disease caused by a virus in the paramyxovirus family. It infects the respiratory tract, then spreads throughout the body. In 2018, it caused more than 140,000 deaths, mainly in children under 5, despite the availability of a safe and effective vaccine. Routine measles vaccination for children, combined with mass immunization campaigns in countries with high case rates and death rates, are key public health strategies to reduce global measles deaths.⁵

The measles vaccine has long been observed in association with pronounced non-specific protective effects against contagious diseases.^6,7 When the measles vaccine was introduced in 7 African countries, the overall mortality in children of those countries declined by 30% to 86%, a reduction far larger than anticipation based on the protection against deaths caused by measles alone.⁶ A random controlled trial found that the measles vaccine was associated with a 30% reduction in overall mortality in children. Among these, only 4% could be explained by prevention of measles infection.⁷

The vaccine is an efficient, live attenuated, replicating virus. It has been safely administered to 2 billion children over the last 40 years, affording life-long protection after a single dose.⁸ These advantages made the vaccine a popular vaccine vector candidate to be genetically engineered. In the last few years, scientists have genetically engineered the measles vaccine and tested the result's protection efficiency against two coronavirus-caused diseases: SARS (Severe Acute Respiratory Syndrome) and MERS (Middle-East Respiratory Syndrome).

In 2014, a recombinant measles vaccine which incorporates and expresses the spike protein (a surface protein mediates attachment of virus) of SARS was constructed.⁹ It was found that the live-attenuated recombinant measles vaccine could induce neutralizing antibodies, and that it protected immunized mice from infection by SARS-CoV.⁹ In 2018, two live-attenuated recombinant measles virus vaccines, either expressing S protein or N protein (structural protein on the surface of virus) of MERS-CoV, were found to induce a robust humoral and cellular immunity response against MERS-S mediating protection in the mouse model.¹⁰

Based on the above experimental results, a genetically-engineered measles vaccine carrying the S or the N protein pf SARS-CoV-2 may be an option to provide protective effects against COVID-19.

MMR (measles, mumps and rubella) vaccine
The MMR vaccine is a combined live attenuated vaccine that helps to prevent measles, mumps and rubella. Research studies of two scientists, Dr Paul Fidel and Prof. Mairi Noverr, in the USA, found that the combined vaccine could induce myeloid-derived suppressor cells (MDSCs). The induction of these cells from bone marrow reduced inflammation and mortality in mouse models.¹¹ Moreover, previous experimental studies showed that MDSCs inhibit septic inflammation.¹² Based on the above findings, the two scientists suggest that the combined vaccine could induce MDSCs in COVID-19 patients and help them to fight the lung inflammation and sepsis which associated with the most serious cases of the disease.¹¹

Adults who received the MMR vaccine as a child will likely still have antibodies against the measles, mumps and rubella viruses, but are unlikely to still have MDSCs, as these cells are not life-long cells. This means they would require a second time injection to reinitiate the MDSCs and obtain the potential benefits against COVID-19.

Besides the experimental evidence, the report from Dr Paul Fidel and Prof. Mairi Noverr cited a recent event that support their hypothesis. The 955 sailors on the U.S.S. Roosevelt who tested positive for COVID-19 had milder symptoms, except for one hospitalization. They suggested that this may have been a consequence of the MMR vaccinations given to all U.S. Navy recruits. However, this may also be the fact that they are young and stronger.¹¹

By genetic data analysis, a team lead by Prof. Robin Franklin at Cambridge University have identified a 29% amino acid sequence homology between the Macro (ADP-ribose-1-phosphatase) domains of SARS-CoV-2 and the rubella virus which is used the MMR vaccine. This provides further preliminary evidence that the MMR vaccine might provide protection against COVID-19.¹³

The MMR vaccine is highly safe. The vaccination of immunocompetent individuals has no contra-indications. A clinical trial of the MMR vaccine in high-risk healthcare workers in New Orleans has been proposed by Dr Paul Fidel and Prof. Mairi Noverr. They have also been awarded a grant to compare the MMR and BCG vaccines in a primate model of COVID-19.¹¹



Although no existing live attenuated vaccine, nor specific vaccine has yet found to be effective in preventing COVID-19, the existing vaccines that induce non-specific protection do have theoretical advantages over a vaccine specific to SARS-CoV-2. If proven to be effective against COVID-19, there is a higher chance the existing vaccine will still able to confer protection by its broad protection effects even when SARS-CoV-2 undergoes mutation. This is because the vaccine's non-specific effect works by boosting a person's immune response in general. By contrast, a vaccine specific to SARS-CoV-2 has a higher chance of losing its efficacy if the virus mutates, leading to antigenic drift.²



* Innate immunity: Live attenuated vaccines provide non-specific protection against lethal infections unrelated to the target pathogen by inducing "trained" non-specific innate immune cells. This improves a host's responses against subsequent infections. This type of non-specific immune response is the first line of defence against infection and is called the innate immune response. Recent reports show that COVID-19 may suppress innate immune responses.14 Therefore, stimulation by live attenuated vaccines could increase resistance to infection by SARS-CoV-2, the causal virus.



References
1. A. Andersen, A.B. Fisker, A. Rodrigues, et al. National immunization campaigns with oral polio vaccine reduce all-cause mortality: A natural experiment within seven randomized trials.Front. Public Health, 2018 Feb 2, 6: 13.
2. K. Chumakov, C.S. Benn, P. Aaby, et al. Can existing live vaccines prevent COVID-19. Science, 2020, vol. 368, Issue 6496, 1187-1188.
3. E. Seppälä, H. Viskari, S. Hoppu, et al. Viral interference induced by live attenuated virus vaccine (OPV) can prevent otitis media. Vaccine, 2011, 29, 8615-8618.
4. M.K. Voroshilova. Potential use of nonpathogenic enteroviruses for control of human disease. Prog. Med. Virol., 1989, 36, 191-202.
5. https://www.who.int/news-room/fact-sheets/detail/measles
6. P. Aaby, B. Samb, F. Simondon, et al. Non-specific beneficial effect of measles immunisation: analysis of mortality studies from developing countries. BMJ, 1995 Aug 19, 311(7003): 481-485.
7. P. Aaby and C.S. Benn. Developing the concept of beneficial non-specific effect of live vaccines with epidemiological studies. Clin. Microbiol. Infect., 2019 Dec., 25(12):1459-1467.
8. P.N. Frantz, S. Teeravechyan, and F. Tangy. Measles-derived vaccines to prevent emerging viral diseases. Microbes Infect., 2018, 20:493-500.
9. N. Escriou, B. Callendret, V. Lorin, et al. Protection from SARS coronavirus conferred by live measles vaccine expressing the spike glycoprotein. Virology. 2014, 452-453:32-41.
10. B.S. Bodmer, A.H. Fiedler, J.R.H. Hanauer, et al. Live-attenuated bivalent measles virus derived vaccines targeting Middle East respiratory syndrome coronavirus induce robust and multifunctional T cell responses against both viruses in an appropriate mouse model. Virology, 2018, 521:99-107.
11. P.L. Fidel and M.C. Noverr. Could an unrelated live attenuated vaccine serve as a preventive measure to dampen septic inflammation associated with COVID-19 infection? mBio, DOI:10.1128/mBio.00907-20
12. S.K. Esher, P.L. Fidel, M.C. Noverr. Candida/staphylococcal polymicrobial intra-abdominal infection: pathogenesis and perspectives for a novel form of trained innate immunity. J. Fungi (Basel), 2019 Jun; 5(2): 37.
13. R. Franklin, A. Young, B. Neumann, et al. Homologous protein domains in SARS-CoV-2 and measles, mumps and rubella viruses: preliminary evidence that MMR vaccine might provide protection against COVID-19. MedRxiv, doi: https://doi.org/10.1101/2020.04.10.20053207
14. M. Zheng, Y. Gao, G. Wang, et al. Functional exhaustion of antiviral lymphocytes in COVID-19 patients. Cell. Mol. Immunol., 2020 May, 17 (5), 533-535.

Coronavirus (17) Limitations of the evidence of COVID-19 prevention from non-specific effects of BCG vaccine

My last blog post introduced the BCG vaccine and its non-specific protective effects. However, we should not be too optimistic about it until a clinical result from a prospective random clinical trial comes out to prove the non-specific protection of BCG against COVID-19. This is because the evidence suggesting BCG vaccine's preventive effect against COVID-19 was drawn mainly from retrospective studies and speculative reports. The claims that universal BCG vaccination in a country results in lower morbidity and mortality rate of COVID-19 in that country, were based on observation and did not account for several factors that could also explain the discrepancies between different places.^1-5 These factors include:

1. Public awareness:
The places with universal BCG vaccination policy such as South Korea, Taiwan and China have also been stricken by different epidemics in recent decades. The SARS outbreak in 2003 affected China, Taiwan and South Korea, while the MERS outbreak in 2015 seriously affected South Korea. Therefore the people and the governments of these countries have more experience and could act quickly in tackling the new infectious disease. This helps in slowing down the spread and lowering the severity of COVID-19.

2. Cultural differences which affect the effectiveness of the non-pharmaceutical interventions being adopted:
Most of the developed countries that do not have universal BCG vaccination, such as USA, UK and Italy, implemented quarantine, social distancing and isolation measures to contain and mitigate COVID-19. However, there is a higher proportion of civilians in these countries that did not obey and even protested against the measures. These reactions will have made the measures less effective.
On the other hand, the higher obedience among Asian people, such as Japanese, Korean and Chinese people, make it easier for the government to enforce the measures to contain the disease. Moreover, most of the people in these areas are conscientious and more willing to put on a face mask whenever they are outside their homes. According to WHO, the use of face masks is one of the measures that can limit the spread of COVID-19.⁶

3. Testing rate:
Within the first month or so from the start of the pandemic, Korea was already able to expand the detection of SARS-CoV-2, with a sensitivity rate of over 95%, to more than 10,000 people a day. This can quickly identify clusters of infections and quarantine the infected individuals.

4. Genetics of the population:
Super-spreaders can ignite a large-scale transmission. The low number of cases and deaths per population in some countries might be due to fewer super-spreaders, which may reflect genetic differences.⁷ Further study is needed to clarify this assumption.

5. Different countries had different onset times, consequently having different positions on the epidemic curve:
The observational studies correlating the BCG coverage with the low morbidity and mortality rate of COVID-19 were made based on the first three months of the outbreak of the disease (January to March). During that period, India and Ethiopia, which have long-standing BCG vaccination policies, were not yet affected by COVID-19. However, these two countries have been hit seriously by the pandemic since May. Therefore it was too early to correlate the BCG coverage with the low severity of COVID-19. The different onset in a pandemic between countries is largely due to the difference in frequency of travelling from the disease's outbreak epicentre, China. More people from China travel to Italy, the UK and the USA than to India and African countries, which had a later onset of the epidemic.

6. The differences in diagnosing and reporting COVID-19 cases:
Developing countries, which usually have BCG vaccination policies against tuberculosis, such as India, Indonesia and the Phillipines, have relatively less advanced medical systems. They have lower testing ability and less efficient reporting systems. This can result in lower morbidity and mortality rates on paper, and does not reflect the real figure.

7. The beneficial off-target effects of the BCG vaccine might be altered by subsequent administration of a different vaccine:⁸
Children are found to be less susceptible to the COVID-19 infection than adults, and their symptoms are generally milder.^9-12 This may be due to the required vaccine programmes for every child having non-specific effects against COVID-19, but not necessarily the BCG vaccine. On the other hand, the beneficial off-target effects of the BCG vaccine might be altered by subsequent administration of different live attenuated vaccines.^8,13

Moreover, it is unlikely that a BCG vaccine given decades ago in childhood could help in preventing COVID-19 nowadays. Whether older people could maintain a pool of trained monocytes many years after BCG vaccination is still questionable. A possible explanation for the observation is that children who have been vaccinated with BCG are less susceptible to infection with SARS-CoV-2 and therefore less likely to spread it to older populations.²

Conclusion
There is evidence that the BCG vaccine has non-specific effects against respiratory infections. However, there is currently no direct evidence that BCG vaccine protects against COVID-19. Hopefully, with the ongoing random clinical trials mentioned in my previous blog post, we can find out the answer in the near future.

If the BCG vaccine could really help in preventing COVID-19, it is important to know 1) which BCG strain is the most effective, as there are about 8 strains of BCG vaccine in the world,^14,15 2) if the BCG vaccine will exacerbate COVID-19 in a minority of patients with severe disease,³ 3) how long could the heterologous protective effect conferred by BCG last after vaccination,¹⁶ and 4) the optimal time in the life to vaccinate.¹⁷

*Examples of countries which do not have a universal BCG vaccination policy: Italy, the USA, Spain, Germany, and the UK. Italy has never had a national BCG programme; BCG is not recommended for generalized use in the US; and others phased theirs out as TB became less of a concern - Spain in 1981, Germany in 1998 and the UK stopped in 2005. ¹⁸ Examples of countries with long-standing universal BCG vaccination policies: South Korea, Japan, India, Ethiopia.¹⁸

References
1. Does BCG vaccination protect against acute respiratory infections and COVID-19? A rapid review of current evidence. CEBM, April 24,2020. https://www.cebm.net/covid-19/does-bcg-vaccination-protect-against-acute-respiratory-infections-and-covid-19-a-rapid-review-of-current-evidence/
2. L.A.J. O'Neill, and M.G. Netea. BCG induced trained immunity: can it offer protection against COVID-19? Nature Reviews Immunology,2020, 20, 335-337.
3. N. Curtis, A. Sparrow, T.A. Ghebreyesus, et al. Considering BCG vaccination to reduce the impact of COVID-19. Lancet, 2020 May 16;395(10236):1545-1546.
4. L. Faust, S. Huddart, E. MacLean, et al. A. Universal BCG vaccination and protection against COVID-19: critique of an ecological study. April 1, 2020. https://naturemicrobiologycommunity.nature.com/users/36050-emily-maclean/posts/64892-universal-bcg-vaccination-and-protection-against-covid-19-critique-of-an-ecological-study
5. C. Ozdemir, U.C. Kucuksezer, and Z.U. Tamay. Is BCG vaccination affecting the spread and severity of COVID-19? Allergy. 2020 Jul;75(7):1824-1827.
6. Advice on the use of masks in the context of COVID-19. Interim guidance. 6 April 2020. World Health Organization. https://apps.who.int/iris/bitstream/handle/10665/331693/WHO-2019-nCov-IPC_Masks-2020.3-eng.pdf?sequence=1&isAllowed=y
7. Akiko Iwasaki, & Nathan D Grubaugh. Why does Japan have so few cases of COVID-19? EMBO Molecular Medicine, 2020, 12: e12481. https://doi.org/10.15252/emmm.202012481
8. A.J. Pollard, A. Finn, and N, Curtis N. Non-specific effects of vaccines: plausible and potentially important, but implications uncertain. Arch Dis Child 2017; 102: 1077-1081.
9. J. Zhang, M. Litvinova, Y. Liang, et al. Changes in contact patterns shape the dynamics of the COVID-19 outbreak in China. Science, 2020 Jun 26;368(6498): 1481-1486.
10. D.F. Gudbjartsson, A. Helgason, H. Jonsson, et al. Spread of SARS-CoV-2 in the Iceland population. N. Eng. J. Med, 2020 Jun 11;382(24): 2302-2315.
11. COVID-19 National Emergency Response Center, Epidemiology and Case Management Team, Korea Centers for Disease Control and Prevention. Coronavirus disease-19: The first 7,755 cases in the Republic of Korea. Osong Public Health and Research Perspectives, 2020 Apr;11(2):85-90.
12. CDC COVID-19 Response Team. Coronavirus disease 2019 in children-United States, February 12-April 2, 2020. Morbidity and Mortality Weekly Report. 2020 Apr;69(14):422-426.
13. N. Curtis, A. Sparrow, T.A. Ghebreyesus, et al. Considering BCG vaccination to reduce the impact of COVID-19. Lancet, 2020 May 16;395(10236): 1545-1546.
14. N. Ritz, W.A. Hanekom, R. Robins-Browne R, et al. Influence of BCG vaccine strain on the immune response and protection against tuberculosis. FEMS Microbiol Rev 2008; 32: 821-841.
15. M. Miyasaka. Is BCG vaccination causally related to reduced COVID-19 mortality? EMBO Molecular Medicine, 2020, Jun 8;12(6):e12661. doi: 10.15252/emmm.202012661.
16. J. Kleinnijenhuis, J. Quintin, F. Preijers. et al. Long-lasting effects of BCG vaccination on both heterologous Th1/T H 17 responses and innate trained immunity. J. Innate Immun., 2014, 6, 152-158.
17. M.G. Hollm-Delgado, E.A. Stuart, & R.E. Black. Acute lower respiratory infection among Bacille Calmette-Guerin (BCG)-vaccinated children. Pediatrics, 2014, 133, e73-e81.
18. A. Zwerling, M.A. Behr, A. Verma, et al. The BCG World Atlas: a database of global BCG vaccination policies and practices. PLoS Med 2011;8(3):e1001012.

Coronavirus (16) Non-specific effects of BCG vaccine to prevent COVID-19?

After reading my blog posts introducing the existing drugs being tested for COVID-19 treatment, you may wonder if there are any existing vaccines being tested for prevention of COVID-19. The answer is yes. This is a vaccine for tuberculosis (TB) called Bacille Calmette Guérin (BCG) which is now being tested in several clinical trials globally.

BCG was developed in France by Albert Calmette and Camille Guérin in order to prevent TB in the last century. The two scientists made use of a strain of bacteria that caused bovine tuberculosis (Mycobacterium bovis), diminished its virulent activity, and applied it to humans.¹ The application of the weakened cattle bacteria induces the generation of antibodies which can also recognize and neutralize the bacteria that causes TB in humans, Mycobacterium tuberculosis. This makes BCG very effective in preventing TB.

However, the cattle bacteria that causes TB is very different from the human virus SARS-CoV-2. The perceived benefit of the BCG vaccine for COVID-19 prevention is not based on the cross neutralizing effect of the antibody generated against the vaccine. Rather, it is the vaccine's ability to initiate an overall boost to the immune system.

BCG is a live attenuated vaccine (live but with substantially weakened virulence activity). For a long time, scientists have observed a phenomena that live attenuated vaccines have "non-specific effects", which means that the protective effect of vaccine can extend to some infectious or inflammatory diseases other than its initial specific target.²

Since the introduction of the vaccine in the 1920s, several studies reported a reduction of neonatal mortality in countries where BCG vaccines are administered to newborns. The reduction rate could not be explained only by the reduction of tuberculosis.³ Later in the 2000s in Guinea-Bissau, a random controlled trial showed that BCG vaccine administered at birth to low-birth-weight infants showed an up-to-50% reduction of mortality in young children. This reduction was suggested to be due to the protection against unrelated infectious agents that cause respiratory tract infections, septicemia (a blood poisoning which occurs when a bacterial infection elsewhere in the body, such as the lungs or skin, enters the bloodstream),⁴ and fever.⁵

Moreover, it seems that the protection from the "non-specific effects" conferred by the administration of BCG is not only limited to newborn children. A study taken from 1971 to 2010 in Denmark showed that BCG given at school entry was associated with a significant reduction in the risk of dying from natural causes before the age of 45 years.⁶ Additionally, a clinical trial giving the BCG vaccine to tuberculin-negative elderly in Japan showed a protection against pneumonia. This demonstrates that the BCG vaccine can also confer non-specific protection when administered late in life.⁷

In fact, an experimental infection provides evidence that the vaccine can reduce the severity of infections by other viruses in vivo. It is demonstrated by the finding that a BCG vaccine given 4 weeks prior to a yellow fever vaccine reduced the viraemia (the presence of a virus in bloodstream) by 71% in volunteers in the Netherlands.⁸ Because of its non-specific effects, the BCG vaccine is also used as adjuvant immunotherapy for patients with non-muscle-invasive bladder cancer, to induce immune-stimulating effects that slow down tumour progression.^9,10

Above are some of the examples of the non-specific effects the BCG vaccine conferred. But how did the BCG vaccine correlate with COVID-19? Since the outbreak of the disease, there is a high heterogeneity of infection and mortality rates across countries, and scientists tried to find out the reasons behind this. One of the hypotheses is the vaccination coverage. When analysing the BCG and another 8 vaccines' coverages in the years of 2018, 2008, 1998 and 1988, in 125 countries around the world, a study found a significant moderate negative correlation between BCG coverage and the number of COVID-19 cases. This means the higher the BCG coverage, the less the number of COVID-19 cases per unit population.¹¹ Some observation speculative reports also found that ratio of COVID-19 cases per population and the ratio of deaths per COVID-19 cases are significantly lower in BCG-vaccinated countries.^12-14

The combination of reduced morbidity and mortality has led to the suggestion that vaccination with BCG might have a role in protecting health-care workers and other vulnerable individuals against COVID-19.

According to the data from the ClinicalTrials.org (a database of privately and publicly funded clinical studies conducted around the world), there are 18 trials registered to test the BCG vaccines on their effectiveness at protection against COVID-19.¹⁵ Among these, eight are currently in progress: randomised controlled trials in the Netherlands, South Africa, Australia, and the USA are to test whether BCG vaccination of health-care workers could protect them from COVID-19; a randomised controlled trial in Greece is to test the effect of BCG vaccination on the prevention of severe COVID-19 infection among older people; two random placebo-controlled trials in Germany are testing a genetically modified BCG vaccine, VPM1002, on health-care workers and older patients, respectively; and a clinical trial in Egypt is to check if COVID-19 cases admitted to hospitals or intensive care units had been vaccinated with BCG before.

These clinical trials are useful for us to understand whether and how the vaccine confers resistance to the causal virus of COVID-19.



References
1. S. Luca, and T. Mihaescu. History of BCG vaccine. Maedica, 2013, 8:53-58.
2. P. Aaby, and C. S. Benn. Developing the concept of beneficial non-specific effect of live vaccines with epidemiological studies. Review. Clin. Microbiol. Infect, 2019, 25(12):1459-1467.
3. Shann, F. The non-specific effects of vaccines. Arch. Dis. Child, 2010, 95, 662-667.
4. https://www.healthline.com/health/septicemia
5. P. Aaby, A. Roth, H. Ravn, et al. Randomized trial of BCG vaccination at birth to low-birth-weight children: beneficial nonspecific effects in the neonatal period? J. Infect. Dis., 2011, 204, 245-252.
6. A. Rieckmann, M. Villumsen, S. Sorup, et al. Vaccinations against smallpox and tuberculosis are associated with better long-term survival: a Danish case-cohort study 1971-2010. Int J Epidemiol., 2017, 46: 695-705.
7. T. Ohrui, K. Nakayama, T. Fukushima, et al. Prevention of elderly pneumonia by pneumococcal, influenza and BCG vaccinations [Japanese]. Nihon Ronen Igakkai Zasshi, 2005, 42, 34-36.
8. R.J.W. Arts, S.J.C.F.M. Moorlag, B. Novakovic, et al. BCG Vaccination protects against experimental viral infection in humans through the induction of cytokines associated with trained immunity. Cell Host Microbe, 2018, 23: 89-100.
9. G. Redelman-Sidi, M.S. Glickman, and B.H. Bochner. The mechanism of action of BCG therapy for bladder cancer-a current perspective. Nat. Rev. Urol. 2014, 11, 153-162.
10. R.F. Han, and J.G. Pan. Can intravesical bacillus Calmette-Guérin reduce recurrence in patients with superficial bladder cancer? A meta-analysis of randomized trials. Urology, 2006, 67, 1216-1223.
11. A. Macedo, and C. Febra. Relation between BCG coverage rate and COVID-19 infection worldwide. Med Hypothesis, 2020 May 6;142:109816.
12. C. Ozdemir, U.C. Kucuksezer, and Z.U. Tamay. Is BCG vaccination affecting the spread and severity of COVID-19? Allergy. 2020;00:1-3.
13. A. Iwasaki, and N.D. Grubaugh. Why does Japan have so few cases of COVID-19? EMBO Molecular Medicine, 2020 May 8;12(5):e12481.
14. A. Miller, M.J. Reandelar, K. Fasciglione, et al. Correlation between universal BCG vaccination policy and reduced morbidity and mortality for COVID-19: an epidemiological study. MedRxiv doi: https://doi.org/10.1101/2020.03.24.20042937
15. https://clinicaltrials.gov/ct2/results?term=bcg&cond=COVID&draw=1&rank=10#rowId9

Coronavirus (15) Dexamethasone: the world's first approved COVID-19 drug (e)

Yesterday in the daily coronavirus briefing, the UK government reported an encouraging finding that dexamethasone reduces the COVID-19 mortality rate, and authorised the use of this drug for severely ill COVID-19 patients who required oxygen, including those on mechanical ventilators.¹ Most of you must have read a lot about the preliminary results from the clinical trial RECOVERY (Randomized Evaluation of COVID-19 Therapy) led by the University of Oxford.² I am not going to repeat what the news has reported these two days. Here I would rather like to explain the mechanism of the drug and explain why it is important not to try to buy the drug and take it home for COVID-19 treatment.

Dexamethasone is a synthetic corticosteroid (steroid) among the most popular drugs being tested for COVID-19. It has been used since 1960 to treat people suffering from a variety of conditions relating to inflammation, such as some skin conditions, arthritis, asthma, and inflammatory bowel disease.

The drug suppresses inflammation by inhibiting the expression of many inflammatory mediators, the cells of the immune system. Severely ill COVID-19 patients who need oxygen suffer from an over-reaction of the immune system, called a cytokine storm, which causes lung injury and multi-organ failure, and can be deadly.³ The suppressive effect on the immune system by dexamethasone helps to calm down the cytokine storm. This explains why the drug can significantly reduce deaths in ventilated patients and the patients in need of oxygen.

The clinical trial result showed that the drug only works in severe cases while having little effect on COVID-19 patients with lesser symptoms of the disease. This is because the patients with less severity are not affected by over-reaction of the immune system. The application of the drug thus has no benefit for these patients.

It is also notable that the clinical trial RECOVERY used "low dose" of the dexamethasone for "up to 10 days" on the patients.² This is because previous experiences showed that higher cumulative doses and longer treatment durations of corticosteroids are more likely to develop osteonecrosis in SARS patients.⁴ In fact, in general practice, clinicians would avoid long-term prescription of the drug, and the drug tapered quickly if the patient is improving.⁵

The drug has no life-threatening side effects. However, patients with chronic use of the drug are usually monitored for mood changes, development of osteoporosis, weight gain, hyperglycemia, electrolyte changes, and depression.⁵ Moreover, the use of the drug is contraindicated if patients have systemic fungal infections, hypersensitivity to dexamethasone, or cerebral malaria.⁵

In addition to the side effects it can cause and the contraindication, the use of the drug in early treatment of patients infected with coronaviruses has shown association with a higher subsequent plasma viral load.^6,7 This seems to indicate that the drug's ability to reduce the immune response could also reduce the inflammatory response and prolong the viral load.

The drug is cheap and people can buy the drug on prescription for use with other conditions. However, we should not try to buy it and take it home for COVID-19 treatment, as it showed no effect on patients with no critical symptoms. Even for the severely ill patients, the right dose, the right timing, the right length of treatment, and the knowledge of the contraindications are important if the drug is to be beneficial to the patients.

References

1. "World first coronavirus treatment approved for NHS use by government" Department of Health and Social Care, UK, 16 June, 2020. https://www.gov.uk/government/news/world-first-coronavirus-treatment-approved-for-nhs-use-by-government

2. Low-cost dexamethasone reduces death by up to one third in hospitalised patients with severe respiratory complications of COVID-19. RECOVERY news, 16 June 2020. https://www.recoverytrial.net/news/low-cost-dexamethasone-reduces-death-by-up-to-one-third-in-hospitalised-patients-with-severe-respiratory-complications-of-covid-19

3. X. Zhang, Y. Tan, Y. Ling, et al. Viral and host factors related to the clinical outcome of COVID-19. Nature, 2020 May 20. doi: 10.1038/s41586-020-2355-0

4. R. Zhao, H. Wang, X. Wang, et al. Steroid therapy and the risk of osteonecrosis in SARS patients: a dose-response meta-analysis. Osteoporos Int, 2017 Mar;28(3):1027-1034.

5. D.B. Johnson, M.J. Lopez, and B. Kelley. Dexamethasone. 2020 Apr 27. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. PMID: 29489240

6. N. Lee, K.C. Chan, S. Hui, et al. Effects of early corticosteroid treatment on plasma SARS-associatedCoronavirusRNA concentrations in adult patients. Journal of Clinical Virology, 31 (2004) 304-309.

7. Y.M. Arabi, Y. Mandourah, F. Al-Hameed, et al. Corticosteroid therapy for critically ill patients with middle east respiratory syndrome. Am J Respir Crit Care Med., 2018; 197: 757-767.

Coronavirus (14) Popular drugs tested for effectiveness in COVID-19 treatment (d)

Continued from a series of my blog posts started from 27th May.
12. Ruxolitinib
Ruxolitinib (Jakafi®, Incyte Corporation, Wilmington, DE, USA) is a Janus Kinase 1 (JAK1)/JAK2 inhibitor approved by the US FDA and European Medicines Agnecy for bone-marrow diseases such as polycythaemia vera (PV) and myelofibrosis (MF), which are characterized by aberrant activation of the JAK-STAT pathway.¹

Severe COVID-19 patients develop cytokine storm due to overreaction of the immune system. Many cytokines, including IL-2, IL-6, IL-7, IL-10, G-CSF, GM-CSF, and IFN gamma, are implicated in COVID-19-associated cytokine storm via the JAK-STAT pathway.^2,3,4 Therefore, compared with molecules that target to only a single cytokine or cytokine receptor, JAK inhibitors, including ruxolutinib, have the potential advantage of inhibiting the activity of multiple cytokines simultaneously.

On the basis of the above hypothesis, a randomised, multi-centre, placebo-controlled, single-blind phase 2 trial in 43 hospitalized patients with severe COVID-19 were first conducted in China to evaluate the efficacy and safety of ruxolitinib for COVID-19.⁵ Although no statistical difference from the placebo group was observed, ruxolitinib recipients had numerically faster clinical improvement including significant chest CT improvement, faster recovery from lymphopenia, and favourable side-effect profile.

A phase 3 clinical trial of ruxolitinib, RUXCOVID (NCT04331665), launched by Incyte and Novartis will be started soon. The study is to evaluate the safety and efficacy of ruxolitinib in people diagnosed with COVID-19 pneumonia by determining the number of people whose conditions worsen (requiring machines to help with breathing or needing supplemental oxygen) while receiving the drug.⁶

As mentioned above, JAK inhibitors can inhibit a variety of inflammatory cytokines. This can also inhibit some cytokines which play an important role in curbing virus activity, such as interferon alpha.⁷ Therefore, detailed analysis of ruxolitinib for its efficacy and safety is very important.

13. Enoxaparin
Enoxaparin (Lovenox) is a low molecular weight heparin (LMWH), an anticoagulant (blood thinner) which is used to prevent blood clots. High D-dimer level, which indicates significant formation and breakdown of fibrin clots in the body, and cytokine storm, are highly correlated with the severity of COVID-19.^8-10 In fact, thrombosis (a process of blood clot formation) and inflammation processes mutually reinforce each other.^11-13 Therefore, heparins such as enoxaparin, which has anti-inflammatory activity besides the anti-coagulant effects, are tested for their effectiveness in the treatment of severe cases of COVID-19.¹⁴ Moreover, LMWH inhibits heparanase activity, which in turn decreases the transcription of IL-6.^15,16 Enoxaparin may has similar effect.¹⁷

In addition, it was found that heparin interacts with the SARS-CoV-2 spike S1 protein receptor binding domain, thereby attenuating viral attachment and infection.¹⁸ This theoretically suggests that enoxaparin is also useful in COVID-19 prevention.

A retrospective study examining 42 hospitalized COVID-19 patients in China revealed a significant decrease in IL-6 levels in an LMWH treatment group compared with a non-LMWH treatment group (p=0.006).¹⁷

COVID-19 hospitalized patients have a higher possibility of developing venous thromboembolism (VTE), a condition in which a blood clots form, most often in the deep veins of the leg, groin or arm, and travel in the circulation, lodging in the lungs, causing pulmonary embolism.¹⁹ A randomized clinical trial aiming to include 2,712 COVID-19 patients hospitalised on non-intensive care unit, has been approved by the Italian Medicines Agency (AIFA) to compare efficacy (prevention of VTE) and safety (incidence of major/clinically relevant bleeding) of the standard prophylactic dose of enoxaparin with those of a higher dose.²⁰

Enoxaparin is an anticoagulant. Overdose may cause excessive bleeding. Patients should be monitored closely if the drug is applied, as the safety range of the drug is different for different people.

Summary

As we can see from the above list, the drugs being tested range from monoclonal antibodies (e.g. tocilizumab, sarilumab), to steroids (e.g. corticosteroids), nucleic acid analogues (e.g. favipiravir, Remdesivir), and viral protease/polymerase inhibitors (e.g. lopinavir/ritonavir). Their actions range from inhibiting SARS-CoV-2 viral entry (e.g. umifenovir), to inhibiting the viral replication (e.g. chloroquine, hydroxychloroquine, lopinavir/ritonavir, azithromycin, favipiravir, Remdesivir), relieving cytokine storm that occurred in severe COVID-19 cases (e.g. tocilizumab, corticosteroids, INF beta, sarilumab, ruxolitinib), and inhibiting coagulation that may cause blood clotting (e.g. enoxaparin).

The application of these drugs range from preventive to treatment for patients with different severity levels of the disease. Some of the drugs are tested by themselves, while some antiviral drugs, which have no specific activity, are tested in combinations. The clinical trials of these drugs hopefully can find a drug or combination of drugs that can be repurposed for prevention or treatment of COVID-19, with the correct dose and length of the course, before a vaccine becomes available.

It is becoming clear that many patients who are dying with COVID-19 have underlying comorbidities, such as heart or lung problems. Therefore, it is also important to manage the patient’s pre-existing conditions while trying the drugs repurposed for the COVID-19.²¹

Currently, the UK is centrally controlling the supply of drugs that may be relevant for the management of COVID-19. The above drugs are not to be prescribed outside of a trial. This is not only because the efficacy of such drugs is unproven and they all have potential side effects, it is also because some people rely on these medicines to control other illnesses.

References

1. S. Ajayi, H. Becker, H. Reinhardt, et al. Ruxolitinib. Recent Results Cancer Res., 2018; 212:119-32.
2. M. Gadina, M.T. Le, D.M. Schwartz DM, et al. Janus kinases to jakinibs: from basic insights to clinical practice. Rheumatology (Oxford). 2019; 58 (suppl 1): i4-i16. doi:10.1093/rheumatology/key432
3. S. Kang, T. Tanaka, M. Narazaki, et al. Targeting interleukin-6 signaling in clinic. Immunity. 2019;50(4):1007-1023. doi:10.1016/j.immuni.2019.03.026
4. W. Damsky, and B. King. Calming the cytokine storm: the potential role of JAK inhibitors in treating COVID-19. The Dermatologist. 2000, Vol. 8, issue 5.
5. Y. Cao, J. Wei, L. Zou, et al. Ruxolitinib in treatment of severe coronavirus disease 2019 (COVID-19): a multicenter, single-blind, randomized controlled trial. J Allergy Clin Immun. 2020 May 26;S0091-6749(20)30738-7. doi: 10.1016/j.jaci.2020.05.019
6. “Incyte Announces Initiation of Evaluating Ruxolitinib (Jakafi®) as a Treatment for Patients with COVID-19 Associated Cytokine Storm” https://investor.incyte.com/news-releases/news-release-details/incyte-announces-initiation-phase-3-ruxcovid-study-evaluating
7. W. Zhang, Y. Zhao, F. Zhang, et al. The use of anti-inflammatory drugs in the treatment of people with severe coronavirus disease 2019 (COVID-19): The Perspectives of clinical immunologists from China. Clin Immunol. 2020 May; 214: 108393. doi: 10.1016/j.clim.2020.108393
8. N. Tang, D. Li, X. Wang, et al. Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia. J Thromb Haemost., 2020 Apr;18(4):844-847. doi: 10.1111/jth.14768
9. C. Huang, Y. Wang, X. Li, et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 2020; 395: 497–506.
10. P. Sarzi-Puttini, V. Giorgi, S. Sirotti, et al. COVID-19, cytokines and immunosuppression: what can we learn from severe acute respiratory syndrome? Clin Exp Rheumatol 202; 38: 337-342.
11. S.P. Jackson, R. Darbousset, S.M. Schoenwaelder, et al. Thromboinflammation: challenges of therapeutically targeting coagulation and other host defense mechanisms. Blood 2019; 133: 906-918.
12. T.A.M. Claushuis, S.F. de Stoppelaar, I. Stroo, et al. Thrombin contributes to protective immunity in pneumonia-derived sepsis via fibrin polymerization and platelet-neutrophil interactions. J Thromb Haemost 2017; 15: 744-757.
13. J. Bester, C. Matshailwe, and E. Pretorius. Simultaneous presence of hypercoagulation and increased clot lysis time due to IL-1β, IL-6 and IL-8. Cytokine. 2018;110:237-242.
14. M. Marietta, W. Ageno, A. Artoni, et al. COVID-19 and haemostasis: a position paper from Italian Society on Thrombosis and Haemostasis (SISET). Blood Transfus 2020; 18: 167-169. Doi: 10.2450/2020.0083-20
15. I. Vlodavsky, N. Ilan, A. Naggi, et al. Heparanase: structure, biological functions, and inhibition by heparin-derived mimetics of heparan sulfate. Curr Pharm Des. 2007;13(20):2057–2073.
16. A.M. Agelidis, S.R. Hadigal, D. Jaishankar, et al. Viral activation of heparanase drives pathogenesis of Herpes Simplex Virus-1. Cell Rep. 2017;20(2):439–450.
17. C. Shi, C. Wang, H. Wang, et al. The potential of low molecular weight heparin to mitigate cytokine storm in1severe COVID-19 patients: a retrospective clinical study. MedRxiv, 15th April, 2020. doi: https://doi.org/10.1101/2020.03.28.20046144
18. C. Mycroft-West, D. Su, S. Elli, et al. The 2019 coronavirus (SARS-CoV-2) surface protein (Spike) S1 Receptor Binding Domain undergoes conformational change upon heparin binding. BioRxiv preprint. doi: https://doi.org/10.1101/2020.02.29.971093
19. S. Tal, G. Spectre, R. Kornowski, et al. Venous thromboembolism complicated with COVID-19: what do we know so far? Review. Acta Haematologica, 2020 May 12;1-8. doi: 10.1159/000508233
20. Marco Cattaneo, Nuccia Morici. Is thromboprophylaxis with high-dose enoxaparin really necessary for COVID-19 patients? A new “prudent” randomised clinical trial. Blood Transfusion. 2020; 18: 237-238. doi: 10.2450/2020.0109-20
21. "The hunt for an effective treatment for COVID-19." The Pharmaceutical Journal, 9 April, 2020. https://www.pharmaceutical-journal.com/news-and-analysis/features/the-hunt-for-an-effective-treatment-for-covid-19/20207883.article?firstPass=false