Query Response

Responder: Anonymous

That’s still a work in progress. We know the body starts to produce antibodies five to 10 days after infection. We know the immune system follows a pretty standard blueprint like it does for most respiratory viruses— an infection that causes severe symptoms is likely to lead to a stronger immune response, which should encourage strong and longer-lasting immunity in the future. On the flip side, a mild or asymptomatic case is likely to yield lower antibody levels, as was found in covid-19 patients in a new study published in Nature Medicine last month. But it’s not quite clear that antibodies even appear in all cases. A preprint study last month, which measured antibody levels in patients in London, found that between 2% and 8.5% didn’t even develop detectable antibodies. Those in this group who survived infection (typically younger people) likely had to fight off infection through cell-mediated arms of the immune system—white blood cells and cytokines that directly engage and kill pathogens—rather than through antibodies that neutralize the virus. We still don’t know how long immunity lasts (could be only a few months), and if it means people could fall prey to repeated infections. And we’re still not sure what kind of covid-19 immunity we will get from a potential vaccine—whether it’s total or just protection from the worst symptoms. It won’t be until phase III trials (which will directly measure the vaccine’s efficacy) that we'll have a better sense of what the relationship between antibody levels and immunity is, and what sort of immune response a vaccine needs to elicit to provide true protection.