The Latest on Coronavirus and Immunity

There’s a possibility that immunity might not last

In recent weeks, antibody testing has dominated the Covid-19 conversation because of its exciting potential to identify who is immune to the disease. The basic idea is that people who test positive for Covid-19 antibodies must have already been infected, meaning that their immune systems can protect them from reinfection as they step out into the slowly reopening world.

If this sounds too good — and simple — to be true, that’s because it is: There are many caveats to antibody testing and its implications for immunity. Not only does the accuracy of antibody tests vary significantly, but there’s also no guarantee that the presence of antibodies means a person is immune. In its guidance on this point, the World Health Organization cautioned that there’s not enough evidence to say that the presence of Covid-19 antibodies means a person is immune, and it has warned officials not to use results from antibody tests for policy decisions. Furthermore, even if a person does become immune to Covid-19, their immunity might not last.

It’s understandable if these caveats about antibodies and immunity seem confusing. There’s a popular idea that people who are infected with a virus gain immunity as they recover; the thinking is that their immune systems produce antibodies to attack the virus, and those antibodies stay primed and ready to fight the virus the next time it comes along. This is true for some viruses, like…