Besides the problems with sensitivity and reliability of antibody tests for COVID-19,1,2 scientists from WHO issued a warning on the use of these tests, as they thus far do not have enough evidence that a person could be risk free from reinfection even if a positive antibody test result for COVID-19 is correct. This was announced in a news conference at WHO's Geneva headquarters. Their concern is based on two factors, for which they do not yet have answers because the disease has just newly emerged and has been threatening humans for only a few months.3,4
One concern is what level of blood antibody is enough for COVID-19 immunity and protection from reinfection. As mentioned in my last blog, people with severe illness tend to have a quicker and stronger antibody response, while people with mild or no symptoms tend to develop the antibodies slowly and in lower quantities. However, even among the people who developed a strong antibody response and have over 90% chance to be detected by an antibody test, that level of antibodies "does not mean that somebody is immune" said Dr. Maria Van Kerkhove, head of WHO's emerging diseases and zoonosis unit. These tests can detect serological antibodies if they reach the sensitivity level of the test. However, "right now, we have no evidence that the use of a serological test can show that an individual is immune or protected from reinfection."3
The other concern is the duration of protection the antibodies can give to a person who has been infected with SARS-CoV-2. Dr. Mike Ryan, executive director of emergencies program of WHO, said that "nobody is sure whether someone with antibodies is fully protected against having the disease or being exposed again," after his saying that scientists are still determining the length of protection antibodies might give to a person with coronavirus infection history. "With regards to recovery and then reinfection, I believe we do not have the answers to that. That is an unknown."3
The level and the duration of the serological antibody which can protect a previously infected person during the second time of SARS-CoV-2 infection are crucial knowledge in protecting patients. It will take a long time to find out the answers from bigger studies amid the increased number of the cases. Therefore it is better if countries or peoples do not use antibody tests as an indication of immunity before clearer answers emerge. Moreover, even if your antibodies do protect you from becoming sick, you may still harbour the virus and pass it to others.
References
1. "Coronavirus (5) What is RNA test? Antigen test? Or antibody test?" https://yunwenincambridge.blogspot.com/2020/04/coronavirus-5-what-is-rna-test-antigen.html
2. "Coronavirus (7) Abandonment of home-based antibody tests" https://yunwenincambridge.blogspot.com/2020/04/coronavirus-7-abandonment-of-home-based.html
3. "WHO warning: No evidence that antibody tests can show coronavirus immunity" CNBC, 17th April, 2020. https://www.cnbc.com/2020/04/17/who-issues-warning-on-coronavirus-testing-theres-no-evidence-antibody-tests-show-immunity.html
4. "Coronavirus: Double warning over antibody tests" BBC news, 18th April, 2020. https://www.bbc.co.uk/news/uk-52335210
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