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 chickenpox and measles — but not for all of them.
The immune response is not always so black and white. As the New York Times reported on Sunday, it can exist in shades of gray: “Scientists have also repeatedly cautioned that the presence of antibodies does not signify protection from the virus. Some preliminary evidence suggests, for example, that people who are asymptomatic might not produce enough antibodies to prevent a second infection.” It’s not merely the presence of antibodies that confers protection but a certain quantity of antibodies, but scientists don’t know what that quantity is yet, and most antibody tests don’t measure exact amounts. And, as STAT noted, scientists also don’t know whether a person with antibodies can still infect others.
It’s also possible that a person’s immunity to Covid-19 could decrease with time, as Antonio Regalado reported yesterday at the MIT Technology Review. In a study on immunity to common…