For months, the lack of testing for the novel coronavirus in the United States has allowed, ironically, a small glimmer of hope: The official number of COVID-19 cases, currently 957,875, is almost certainly too low.
If people who want to get tested can’t get tested, and if people who are asymptomatic never think to get tested, then it stands to reason that many more Americans must be immune to COVID-19 than presently known. The only way to find the true number is by looking for immunity, which requires testing for proteins called antibodies in the blood that are evidence of past infection. Such antibody tests have been seen as key to reopening the country; other countries have even proposed using them for “immunity certificates” that would allow the immune to return to work.
But if the first results from antibody surveys, also known as “serosurveys,” in the U.S. are anything to judge by, simply not enough people are immune. Too many Americans are still vulnerable to COVID-19 infection for these tests to be the “game changer” that many were hoping for.
A pair of controversial surveys in the Bay Area and Los Angeles County found antibodies in 2.5 to 4 percent of the population—and even those numbers may be overestimates due to methodological flaws. In New York City, the country’s COVID-19 epicenter, 24.7 percent of people tested positive for antibodies. (The statewide number is 14.9 percent.) These rates do translate to many times more cases than officially documented, to be clear, but they are still a far cry from the 70 percent scientists believe is necessary to reach herd immunity and stop disease transmission. And if only a small fraction of the population can return to work without fear of getting the coronavirus, a return to something resembling normal is still a long way off.