Why antibody tests can be unreliable

Antibody tests have given mixed messages to long covid patients. How reliable are they?
11 August 2020

Interview with 

Clare Bryant, University of Cambridge


Covid-19 sample test


Chris Smith asked University of Cambridge immunologist Clare Bryant about why antibody tests have been a false friend for some of these patients…

Clare - Yeah. It's a bit of a disappointment, isn't it. Antibodies, of course, are made over a period of time during the time course of an infection, so timing of the antibody test is absolutely critical. It appears that in the first week of infection, using an antibody test you only pick up about 30% of the people. This is because your antibodies are just beginning to be generated. Then by about weeks 2-3, where the antibody levels are peaking, at that point about 70% of people will positive. After that we're a little unclear, because it depends how long the antibodies last for and how sensitive the antibody test is. It's a little bit disappointing, because one hoped it would be a little bit more clear cut than that, but it's beginning to appear that the antibody test is not going to be the magic silver bullet that our prime minister hoped it would be.

Chris - Researchers in Sweden recently said, well, antibodies are not necessarily the be all and end all; and actually white blood cells - T cells - which also help to fight off infection, play a massively important role, and some people might have no antibodies but lots of T cells. What are they getting at, and would you agree with them?

Clare - Yeah, yeah definitely. I mean, there's two sides to every story with the immune system. So what the T cells do is they detect, pick up, and destroy infected cells. T cells also inform the B cells, and the B cells are the cells that generate the antibodies, so it will also help pile out more antibodies to attack the virus as well. Anything that stimulates T cell response will help with generating protective immunity against this virus. So antibodies and the T cells are actually critical to generating a potentially protective immune response. But again, I say that with the caveat that we hope that this is what's going to happen, and we hope that this is what a vaccine should do, is stimulate antibody responses and T cell responses. But as yet, we don't actually know because we haven't got that data yet.

Chris - If we look at other coronaviruses - because there are four common human coronaviruses that come every winter and they cause common cold-type symptoms - one of them infects cells via exactly the same root as this new coronavirus. So can we get some clues from how the immune system responds to that, to inform what the likely long term response to this new one will be?

Clare - You can get antibodies against that particular coronavirus and that will help protect you against colds for a while. The trouble is the protection doesn't seem to last very long. And so there's a lot of discussion about, if you use a vaccine, will you need to be regularly boosted? If so, how frequently? Because the protection you get against the cold-causing coronaviruses doesn't seem to last for a tremendously long time.


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