When Razani and her co-authors used the phrase “less than 10 percent” in the paper, they did not consider it to be an estimate, she told me. “We were very clear we were not making a summary number,” she said. It was instead a literal description of the other research. Most studies in the review found the share to be below 1 percent. But there was one study that somebody might interpret as suggesting the share of Covid transmission occurring outdoors was close to 10 percent. (In truth, many of those cases involved Singapore construction workers who probably transmitted it in enclosed spaces.) The actual share occurring outdoors is “probably substantially less than 1 percent,” Razani told me. “The outdoors is an amazing resource,” she added. “What we really should be focused on is how to transition more activities to be outdoors.”