What Immunity to COVID-19 Really MeansThe U.S. Food and Drug Administration recently granted an “emergency use authorization” of a blood test for antibodies against SARS-CoV-2, the novel coronavirus that causes COVID-19. It is the first such test to receive approval for the U.S. market. And it comes at a time when health experts and leaders are embracing immunity as a potential end point to the pandemic. In Colorado, a company that makes a coronavirus antibody test has donated kits to the state’s San Miguel County so that everyone there can be tested if they want to. And in Italy, politicians want to use antibody status to determine which people will get “back to work” passes.
Several ambitious surveys to test for these antibodies have now been launched around the globe. The World Health Organization’s Solidarity II study will pool antibody data from more than half a dozen countries. In the U.S., a collaborative multiyear project aims to provide a picture of nationwide antibody prevalence. Its first phase is already collecting samples from blood donors in six major urban areas, including New York City, Seattle and Minneapolis. And the effort will evolve into three national surveys of donors, supported by the Centers for Disease Control and Prevention and conducted this fall and in the fall of 2021.
Unlike diagnostic tests, which are used to confirm the presence and sometimes load, or amount, of the virus, antibody tests help determine whether or not someone was previously infected—even if that person never showed symptoms. Widespread use of such assays could give scientists greater insight into how deadly the virus is and how widely it has spread throughout the population.
It is less clear what those antibody tests mean for real life, however, because immunity functions on a continuum. With some pathogens, such as the varicella-zoster virus (which causes chicken pox), infection confers near-universal, long-lasting resistance. Natural infection with Clostridium tetani, the bacterium that causes tetanus, on the other hand, offers no protection—and even people getting vaccinated for it require regular booster shots. On the extreme end of this spectrum, individuals infected with HIV often have large amounts of antibodies that do nothing to prevent or clear the disease.