“I think there was a lot of hope that we would do the antibody testing or do the serosurveys and then we would see there was a huge amount of immunity built up in the population,” Natalie Dean, a biostatistician at the University of Florida, told me. But earlier data from outside the U.S. have suggested otherwise. One study in the hard-hit municipality of Gangelt, considered “Germany’s Wuhan,” found 14 percent of people testing positive for antibodies. “It was clear from that point, for me, that we weren’t going to see big numbers,” Dean said.

The idea of reopening the country based on antibody tests runs into the technical limits of the tests themselves. Scientists don’t know exactly how long immunity to COVID-19 will last and what level of antibodies confers immunity. “There are just unknowns for an individual,” Gigi Gronvall, a senior scholar at the Johns Hopkins Center for Health Security and a co-author of a recent report on antibody testing, told me. “The ‘get out of jail free’ card we’re hoping for, it’s just not how it should be sold,” she said. The World Health Organization on Friday warned that issuing “immunity certificates” based on antibody testing would be premature.

Meanwhile, a flood of new test kits with varying rates of accuracy is now hitting the market. In the U.K., for example, Prime Minister Boris Johnson touted finger-prick antibody tests as a “game changer,” only for the government to realize that the 3.5 million tests it bought from China were not reliable enough to use. Of particular concern here is the false-positive rate: If the prevalence of COVID-19 is quite low in the population—say, 5 percent—and a test can identify people who are truly negative with 95 percent reliability, half of the “positives” it returns will be false positives. In other words, half of the people the test says have antibodies wouldn’t actually have them. “I wouldn’t want to tell a nurse or physician ‘Go back to work’ based on that,” Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told me.

Read: The U.K.’s coronavirus ‘herd immunity’ debacle

Moreover, Osterholm said, antibody tests don’t give a snapshot of the present. It can take two weeks for a patient to develop a detectable amount of antibodies in their blood, so antibody surveys are necessarily backward-looking. But when public-health officials are deciding whether schools or businesses are safe to reopen, the key piece of information is the number of people currently infected. “I want to know what is happening now,” Osterholm said, “and antibody testing will not get that to you.”

The key strategies for stopping the disease are still the same ones experts have been promoting from the beginning: testing, contact tracing, isolating for those who test positive for COVID-19, and social distancing for everyone else. “There’s going to have to be some level of new normal for a while,” Dean said. Ongoing antibody surveys will help clarify the true scope of the pandemic and the true proportion of asymptomatic carriers, and those data can indeed help inform public-health decisions. But as far as antibody testing goes, Gronvall said, “it’s not the silver bullet for everything.”