In April of 2022, almost two and a half years into the pandemic, the Centers for Disease Control and Prevention estimated that 40 percent of the US population had yet to contract SARS-CoV-2, the virus that causes COVID-19. Thanks to the highly transmissible BA.5 variant, that percentage is probably smaller now, but there are still some people who don’t seem to have ever had an infection—or at least, they’ve never had symptoms or tested positive. SARS-CoV-2 infections can be totally asymptomatic, and the variant in question as well as other factors can influence testing accuracy, raising the possibility that a person could have had COVID-19 and not been aware of it. In addition to leaving many wondering whether they’ve actually caught the virus, this kind of uncertainty also causes headaches for epidemiologists, especially those who want to track community spread.
Generally, testing for prior infections involves looking for antibodies that ...
