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Rapid response to:

Editor's Choice

Covid 19: Where’s the strategy for testing?

BMJ 2020; 369 doi: https://doi.org/10.1136/bmj.m2518 (Published 26 June 2020) Cite this as: BMJ 2020;369:m2518

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Rapid Response:

Re: Covid 19: Where’s the strategy for testing? - Antibody testing might have value as we learn more

Dear Editor

I hope you will forgive me for taking a second bite at this cherry, having already submitted a rapid response relating to PCR testing for Covid-19.

This time I would like to focus on antibody testing.

We have been advised that immunity from other coronaviruses - SARS, MERS, and common cold viruses - appears to be shortlived and not reliably protective. Because of this, we have been appropriately cautious about interpreting antibody test results.

There remains much work to be done on evaluating whether, and for how long, people will have protective immunity following Covid-19 infection - and, if some people do get protective immunity, what proportion of the population will get it.

Increasingly, however, studies are finding that people with Covid-19 do appear to develop protective immunity. Some studies have shown a T-cell response, likely to provide ongoing immunity (even without necessarily having an antibody response); others have shown that many patients develop neutralising antibodies.

Of course, we will have to wait for more time to go by, before we properly understand the immunity that people have post Covid-19 infection. And part of that will be, understanding the antibody results.

However, it seems entirely plausible that people with antibody levels above a protective threshold will have protection. It may be that a qualitative element, looking at the nature of the antibodies, might be required. And we will have to continue to monitor a sample of people who have been tested to see if antibody levels and other markers of immunity decay over time.

So, it may be too soon to be confident in our interpretation of the test results; but it may be that will be able to tell people, retrospectively, that if they had, say, antibodies above a threshold, they are likely to have protective immunity that will last for at least x months...

This might be very useful - particularly, for example, for people who are shielding, but who think they may already have Covid-19. They will have to make difficult decisions about how much contact to have with others; and they might, reasonably, wish to take such findings into consideration.

(With apologies for typos and infelicities - this really is a RAPID rapid response.)

Competing interests: No competing interests

26 June 2020
Peter M B English
Public Health Physician
N/A - this is a personal response
Surrey, UK