[EXPERT REACTION] WHO’s warning on antibody tests and immunity

WHO Director-General Tedros Adhanom Ghebreyesus (Photo: WHO/Twitter)

The World Health Organization (WHO) had issued a warning on Friday about COVID-19 testings, saying that there is no evidence antibody tests can show whether a person has immunity or is no longer at risk of becoming reinfected.

Here are some of the comments collected by our SMC partner in the UK:


Prof Chris Dye, Oxford Martin School, University of Oxford, said:

“The WHO are right to highlight that any antibody test, if we get one, won’t be able to definitely say whether someone is immune to the infection, because we just don’t know enough yet about how immunity works with COVID-19.

“An antibody test (blood test) will only detect infections after the immune system has produced antibodies that recognise the virus. This happens approximately 7–10 days after symptoms develop. There is substantial work ongoing to develop accurate antibody tests for coronavirus infection. To be useful in reporting past infection and immunity in individuals, these new tests must fulfil three criteria.

“First, if some people do not produce detectable amounts of the antibody used in the test after infection, or if antibody levels wane with time, the test will be insufficiently sensitive, missing too many infections (false-negative results) to be useful.  Second, the test must be specific enough to give high confidence that a positive test result is correct (not a false positive). This is especially true if past infection is uncommon among those who are tested, as in the general population. Infection is likely to be more common among people at higher risk, such as health workers.

“Third, before an antibody test can be used to indicate that someone is immune to further infection, the level of protection must be demonstrated in experimental trials. While there is a clear link between the presence of the antibody and protective immunity for many common viral infections, this has not yet been confirmed for the new coronavirus.  It is possible that people are temporarily protected against reinfection but the protection wanes with time, or that protection operates against current but not future strains of the new coronavirus.

“For all these reasons, antibody tests are likely to be most useful for studying past infection in whole populations to assess the scale and spread of the COVID-19 outbreak.

“For more information on testing see here: https://coronavirusexplained.ukri.org/en/article/vdt0006/

Prof Babak Javid, Principle Investigator, Tsinghua University School of Medicine, Beijing and Consultant in infectious diseases at Cambridge University Hospitals, said:

“Strictly speaking, the WHO is correct. Serological tests, which measure antibody responses to SARS-CoV2, do not measure whether those antibodies are able to protect individuals from re-infection. That would require measurement of ‘neutralizing antibody responses’, which are not feasible for commercial testing of large numbers of people. Nor do we know what level of neutralizing antibody responses, even if we were to measure them, would be sufficient for protection, and for how long. Furthermore, any test, to be useful, would need to be highly specific, i.e. the test would need to measure antibodies to SARS-CoV2 and not measure antibodies to common cold coronaviruses. Otherwise, there is the risk of over-estimating the numbers of people who have had Covid-19.

“However, we know from common cold coronaviruses that total antibody responses do approximate (not perfectly) with neutralizing antibody responses. Furthermore, immunity to common cold coronavirus has been experimentally verified with human re-challenge studies (in 1970s and 1980s), and again, correlates with magnitude of the antibody response. So there is a reasonable scientific rationale that a good serological test may be useful. What is urgently needed is first of all identifying a high-quality test that is very specific. Once that is available, longitudinal studies, i.e. measuring antibody responses from the same individual over time will give us an idea how long antibody responses last. Correlating with neutralizing antibody responses in a research lab, as well as ‘relative protection’ by different levels of antibody (which should be feasible in an ongoing pandemic) will strengthen the case that antibody tests can guide probable immunity, and for how long.”

Prof Gary McLean, Professor in Molecular Immunology, London Metropolitan University, said:

Are the WHO saying antibody tests don’t work very well at all?

“They are saying that the antibody test measures evidence of past infection that the immune response has been triggered by the virus – it’s a marker of having been infected.

Or are they saying antibody tests could still be useful for some things but that it’s the level of immunity that infection leads to that is still unknown?

“Yes the test does not prove the immunity is protective – in fact we still don’t know what kind of immunity is needed to stop SARS-CoV2 – it may be antibodies and T cells.

What do we know from evidence so far on COVID-19 about how long immunity lasts after infection?

“Studies have not gone on for much duration yet.  We know the antibodies last for 40-50 days, or at least are still there at convalescence.  It is suspected that antibody protection could last for over one year but this is presumptive.

Is there anything we can know from SARS or from other coronaviruses about likely immunity after infection?

“Yes, SARS is the closest and likely to yield the most information.  The best guess on SARS-CoV2 immunity would come from similar viruses.  We have heard that antibodies protecting against SARS can last for many years and some SARS antibodies do cross react with the current strain.”

* The relevant question asked on Friday at the WHO’s press conference and the answers given can be watched at this link; skip to 28:57: https://www.who.int/emergencies/diseases/novel-coronavirus-2019

**All previous posts about COVID-19 here: https://sciencemediacentremalaysia.com/tag/covid-19/  

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