How large a gathering is too large during the coronavirus pandemic?
A question has perplexed public officials trying to curb the COVID-19 pandemic: How large of a group of people is too large? As the spread of the coronavirus has gathered speed, U.S. officials urged limits on large gatherings, constantly scrambling to reduce the definition of “large.” First, meetings of more than 1,000 were discouraged, then 250, 100, 50 and 10. As many states institute orders to stay at home, all nonessential gatherings are being banned. But no scientific rationale has been cited for any particular number. Getting the right answer is crucial. Too large and you don’t control the epidemic. Too small, and people’s lives and livelihoods may be upended, for insufficient social benefit. “I am not aware of any quantitative modeling informing those decisions,” says Lydia Bourouiba, a physicist and epidemiologist at MIT. “They weren’t based on events.” Now, a new study is providing one roadmap for coming up with an answer. There is no gathering size that can eliminate all risk. But there...