Coronavirus (35) Protein subunit vaccine to COVID-19: an introduction
Since the rollout of the vaccination against COVID-19 in last December, over 15 million people in the UK have received at least one dose. According to the NHS website, reports of serious side effects, such as allergic reactions, have been very rare. No long-term complications or death caused by vaccination have been reported.1
So far, I have introduced in my blog three different types of COVID-19 vaccine in different stages of development: inactivated vaccine, non-replicating viral vector vaccine, and mRNA vaccine. Today in this blog post, I am going to introduce to you another type of vaccine for COVID-19: the protein subunit vaccine, also called protein based vaccine or recombinant protein-based vaccine. The information is mainly from the National Institute of Allergy and Infectious Diseases (NIAID) of the US National Institute of Health (NIH) and Centers for Disease Control and Prevention (CDC).2,3
What is a protein subunit vaccine?
A protein subunit vaccine contains harmless pieces of protein from a viral or bacterial pathogen. These fragments of proteins are identified as the best part of the pathogen to produce a strong and effective immune response. Once vaccinated, the protein subunit triggers the immune system in our body to make T-lymphocytes and antibodies that fight against and remember the protein subunit. Later, when there is infection from the real pathogen, the body can recognize the protein subunit on the pathogen and respond quickly to kill the whole pathogen. For the protein subunit vaccines against COVID-19, most of them are either Spike glycoprotein (S protein) on the surface of the SARS-CoV-2, or the receptor-binding domain (RBD) fragment of a region on the S protein that binds to the receptors of a host cell.2,3
What are the advantages and disadvantages of protein subunit vaccines?
Since protein subunit vaccines include only the components, but not the entire pathogen, this minimizes the risk of side effects. This is best illustrated using of the pertussis (whooping cough) vaccine, which contains components of purified Bordetella pertussis (B. pertussis, the bacteria that cause whooping cough), in 1996. Since the use of the protein subunit vaccine against B. pertussis, to replace the inactivated, whole-cell pertussis vaccines which have been introduced since the 1940s in the United States, the adverse reactions such as fever and swelling at injection site rarely happen. Moreover, the pertussis vaccines containing only protein subunits of B. pertussis have similar efficacy as the traditional inactivated ones.2
However, the precision has its downsides. The protein subunit vaccines most probably do not contain molecular structures called pathogen-associated molecular patterns, which can be read by immune cells and recognized as danger signals. Moreover, the protein subunit may only trigger antibody-mediated immune responses, but not the complete immune responses. Both of these two factors result in an immune response weaker than using the whole-cell vaccines. In order to overcome the problems, protein base vaccines are usually delivered with adjuvants, agents that enhance the immune system. Additionally, booster doses are often required.4
Protein subunit vaccines are made by inserting genetic code for the antigen into living organisms such as bacteria and yeast. The whole manufacturing process requires strict hygiene to avoid contamination with other organisms. This makes them more expensive to produce than chemically-synthesised vaccines, such as mRNA or DNA vaccines. The amount of available protein subunit expands as the bacteria or yeast grows. The final protein subunit vaccine contains the protein subunit extracted and purified from the bacteria or yeast, and other vaccine components such as preservatives to keep it stable, plus adjuvant to enhance the immune response. 4
Protein subunit vaccines are classical vaccines which are already in widespread use, such as the protein subunit vaccines to prevent hepatitis B and human papillomavirus (HPV) infections, which have been used since 1986 and the early 1990s respectively.4 Therefore the technology in developing and manufacturing protein subunit vaccines should be very mature and reliable by now. Moreover, there is no report of serious incident due to this type of vaccine throughout over 30 years of history, showing they are safe.
Below is a list summarizing the advantages and disadvantages of protein subunit vaccines:4
1. The technology is well established. It is a reliable and safe vaccine platform.
2. Suitable for people with compromised immune systems, as no live components are involved in the vaccine. No risk of the vaccine triggering the disease.
3. Relatively stable compared to mRNA and DNA vaccines.
4. Relatively complex and expensive to manufacture compared to the synthesized vaccines.
5. Adjuvants and booster shots may be required.
6. Time needs to spend in determining the best antigen combination.
Thus far, there are 23 protein subunit COVID-19 vaccines in clinical trials (out of a total of 70 COVID-19 vaccines in clinical trials); two of them are in Phase 3 clinical trials.5 One is by Novavax and the other is by a biopharmaceutical company in China. In my next blog post I’m going to introduce to you the vaccine by Novavax which had an interim report of the Phase 3 clinical study published at the end of last month.6
References
1. Coronavirus (COVID-19) vaccine. NHS website. https://www.nhs.uk/conditions/coronavirus-covid-19/coronavirus-vaccination/coronavirus-vaccine/
2. Vaccine types. Subunit vaccines. NIAID website. https://www.niaid.nih.gov/research/vaccine-types.
3. Understanding how COVID-19 vaccines work. CDC website. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/how-they-work.html
4. What are protein subunit vaccines and how could they be used against COVID-19? Gavi, The Vaccine Alliance website. https://www.gavi.org/vaccineswork/what-are-protein-subunit-vaccines-and-how-could-they-be-used-against-covid-19
5. Draft landscape and tracker of COVID-19 candidate vaccines. WHO. https://www.who.int/publications/m/item/draft-landscape-of-covid-19-candidate-vaccines
6. Covid-19: Novavax vaccine shows 89% efficacy in UK trials. BBC News, 29 January, 2021. https://www.bbc.co.uk/news/uk-55850352
Since the rollout of the vaccination against COVID-19 in last December, over 15 million people in the UK have received at least one dose. According to the NHS website, reports of serious side effects, such as allergic reactions, have been very rare. No long-term complications or death caused by vaccination have been reported.1
So far, I have introduced in my blog three different types of COVID-19 vaccine in different stages of development: inactivated vaccine, non-replicating viral vector vaccine, and mRNA vaccine. Today in this blog post, I am going to introduce to you another type of vaccine for COVID-19: the protein subunit vaccine, also called protein based vaccine or recombinant protein-based vaccine. The information is mainly from the National Institute of Allergy and Infectious Diseases (NIAID) of the US National Institute of Health (NIH) and Centers for Disease Control and Prevention (CDC).2,3
What is a protein subunit vaccine?
A protein subunit vaccine contains harmless pieces of protein from a viral or bacterial pathogen. These fragments of proteins are identified as the best part of the pathogen to produce a strong and effective immune response. Once vaccinated, the protein subunit triggers the immune system in our body to make T-lymphocytes and antibodies that fight against and remember the protein subunit. Later, when there is infection from the real pathogen, the body can recognize the protein subunit on the pathogen and respond quickly to kill the whole pathogen. For the protein subunit vaccines against COVID-19, most of them are either Spike glycoprotein (S protein) on the surface of the SARS-CoV-2, or the receptor-binding domain (RBD) fragment of a region on the S protein that binds to the receptors of a host cell.2,3
What are the advantages and disadvantages of protein subunit vaccines?
Since protein subunit vaccines include only the components, but not the entire pathogen, this minimizes the risk of side effects. This is best illustrated using of the pertussis (whooping cough) vaccine, which contains components of purified Bordetella pertussis (B. pertussis, the bacteria that cause whooping cough), in 1996. Since the use of the protein subunit vaccine against B. pertussis, to replace the inactivated, whole-cell pertussis vaccines which have been introduced since the 1940s in the United States, the adverse reactions such as fever and swelling at injection site rarely happen. Moreover, the pertussis vaccines containing only protein subunits of B. pertussis have similar efficacy as the traditional inactivated ones.2
However, the precision has its downsides. The protein subunit vaccines most probably do not contain molecular structures called pathogen-associated molecular patterns, which can be read by immune cells and recognized as danger signals. Moreover, the protein subunit may only trigger antibody-mediated immune responses, but not the complete immune responses. Both of these two factors result in an immune response weaker than using the whole-cell vaccines. In order to overcome the problems, protein base vaccines are usually delivered with adjuvants, agents that enhance the immune system. Additionally, booster doses are often required.4
Protein subunit vaccines are made by inserting genetic code for the antigen into living organisms such as bacteria and yeast. The whole manufacturing process requires strict hygiene to avoid contamination with other organisms. This makes them more expensive to produce than chemically-synthesised vaccines, such as mRNA or DNA vaccines. The amount of available protein subunit expands as the bacteria or yeast grows. The final protein subunit vaccine contains the protein subunit extracted and purified from the bacteria or yeast, and other vaccine components such as preservatives to keep it stable, plus adjuvant to enhance the immune response. 4
Protein subunit vaccines are classical vaccines which are already in widespread use, such as the protein subunit vaccines to prevent hepatitis B and human papillomavirus (HPV) infections, which have been used since 1986 and the early 1990s respectively.4 Therefore the technology in developing and manufacturing protein subunit vaccines should be very mature and reliable by now. Moreover, there is no report of serious incident due to this type of vaccine throughout over 30 years of history, showing they are safe.
Below is a list summarizing the advantages and disadvantages of protein subunit vaccines:4
1. The technology is well established. It is a reliable and safe vaccine platform.
2. Suitable for people with compromised immune systems, as no live components are involved in the vaccine. No risk of the vaccine triggering the disease.
3. Relatively stable compared to mRNA and DNA vaccines.
4. Relatively complex and expensive to manufacture compared to the synthesized vaccines.
5. Adjuvants and booster shots may be required.
6. Time needs to spend in determining the best antigen combination.
Thus far, there are 23 protein subunit COVID-19 vaccines in clinical trials (out of a total of 70 COVID-19 vaccines in clinical trials); two of them are in Phase 3 clinical trials.5 One is by Novavax and the other is by a biopharmaceutical company in China. In my next blog post I’m going to introduce to you the vaccine by Novavax which had an interim report of the Phase 3 clinical study published at the end of last month.6
References
1. Coronavirus (COVID-19) vaccine. NHS website. https://www.nhs.uk/conditions/coronavirus-covid-19/coronavirus-vaccination/coronavirus-vaccine/
2. Vaccine types. Subunit vaccines. NIAID website. https://www.niaid.nih.gov/research/vaccine-types.
3. Understanding how COVID-19 vaccines work. CDC website. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/how-they-work.html
4. What are protein subunit vaccines and how could they be used against COVID-19? Gavi, The Vaccine Alliance website. https://www.gavi.org/vaccineswork/what-are-protein-subunit-vaccines-and-how-could-they-be-used-against-covid-19
5. Draft landscape and tracker of COVID-19 candidate vaccines. WHO. https://www.who.int/publications/m/item/draft-landscape-of-covid-19-candidate-vaccines
6. Covid-19: Novavax vaccine shows 89% efficacy in UK trials. BBC News, 29 January, 2021. https://www.bbc.co.uk/news/uk-55850352
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