Dozens of antibody tests for the novel coronavirus have become available in recent weeks. And early results from studies of such serological assays in the U.S. and around the world have swept headlines. Despite optimism about these tests possibly becoming the key to a return to normal life, experts say the reality is complicated and depends on how results are used.
…[O]verestimates of COVID-19’s spread could lead to underestimates of fatality and hospitalization rates—or excessive confidence about herd immunity. Such immunity is currently thought to require about 70 percent of the population to have been exposed—a rate even hotspots such as New York are likely nowhere near. Any of these errors could, in turn, lead to policies that are bad for public health.
Furthermore, overestimating the prevalence of people with SARS-CoV-2 antibodies could create an unwarranted sense of security about the diagnostic role tests can play. Because false positives are more common in places with low disease prevalence, [epidemiologist Tara] Smith notes, “there is the potential for individuals to be misled regarding their [antibody] status. If they are false positive, they may believe they are immune when they are not and may relax protective measures.”