This week, the US passed a grim milestone in the ongoing coronavirus crisis: 500,000 deaths, more than the number of Americans killed in World War II, the Korean War, and the Vietnam War combined. And yet there is a growing sense of hope that the worst might now be behind us. With new cases declining and immunizations accelerating—45.2 million people have so far received at least one dose of a Covid-19 vaccine, including 20.6 million who have been fully vaccinated—many Americans are beginning to allow themselves to imagine what post-pandemic life might be like.
Achieving that is likely to take a few more months—provided vaccine makers don’t hit any production snags and worrisome variants don’t derail current progress. In the interim, an increasing number of people will find themselves in a liminal state, navigating what it means to be a vaccinated person moving through an unvaccinated world. What are its rules, and what will it take to be a good citizen of it? Answering those questions means confronting an even more fundamental unknown. A vaccinated person may be well-protected from the worst ravages of Covid-19. But it’s not clear if they can still carry the coronavirus and transmit it to susceptible people around them.
This week, two new studies—neither of which have yet gone through peer review—made splashy headlines about the extent to which vaccines slash viral spread. The first, a leaked manuscript first reported by Israeli news site Ynet before being covered by MIT Technology Review, Bloomberg, The Financial Times, and Vox, found that two doses of Pfizer-BioNTech’s shot drove an 89.4 percent drop in infections—both symptomatic and asymptomatic—among vaccinated people in Israel. Though they did not directly measure transmission, the study’s authors—researchers from the Israel Ministry of Health, Hebrew University, and Pfizer—stated in the abstract that the Pfizer vaccine “was highly effective in preventing SARS-CoV-2 infections.” Subsequent news coverage hailed it as the first evidence from the real world that the vaccine could strongly suppress spread of the virus. But scientists not associated with the study say that was an overstatement. (Indeed, Bloomberg later updated its story to include such criticisms, though not the headline.)
In the report, which WIRED has obtained, the research team analyzed aggregated data from Israel’s national testing and disease surveillance system, comparing infection rates in vaccinated versus unvaccinated groups of people between January 17 and February 6. However, as the study authors noted, the ministry’s testing recommendations exempt vaccinated people from requirements like getting tested after travel or being exposed to a known Covid case. Under these protocols, unvaccinated people aren’t just required to get tested more often, they might also choose to, because they’re more worried about contracting Covid-19 than people who’ve gotten the jab. And because infections—especially asymptomatic ones—are more likely to be detected in the group that’s testing more frequently, the estimated 89.4 percent transmission-blocking effect of the vaccine is almost certainly too optimistic (a caveat the authors acknowledged, saying more research is needed to confirm their findings).
“The testing rates were such a hodgepodge, I don’t know you can make any conclusions about how much the vaccine cut transmission in Israel, let alone assigning a number as concrete as 89.4 percent,” says Eric Topol, a professor of molecular medicine at the Scripps Research Institute. The only way to do a careful study of asymptomatic spread and how well the shots curtail it, he says, is to swab both groups—vaccinated and unvaccinated people—every day, ideally for months. Though perhaps prohibitively expensive, the most rigorous version of that experiment would be to also follow each positive test up with contact tracing and genomic sequencing to confirm the route of transmission. The way the Israeli team did it is not the way to get the answer, he says: “It’s a way to get a lot of interest, because everybody wants to hear this.”
Indeed, right on cue, a few hours after the Israeli study began making the rounds in American media, one of my family members sent it to me. Just a few days prior, this person—who is vaccinated with the Pfizer shot—had asked me how safe it would be to fly and immediately join a pod of unvaccinated relatives. They did not like my answer (probably still risky, but we really don’t know just how risky just yet). They liked the Israeli study’s answer much better.