have already dropped mask mandates and fully reopened indoor and outdoor venues, even for large sporting events. New York still has mask requirements.
On Tuesday morning, the health and human services secretary Xavier Becerra said on “CBS This Morning” that he hoped the new guidelines would incentivize people to get vaccinated.
“The message is clear: You’re vaccinated, guess what, you get to return to a more normal lifestyle,” he said. “If you’re not vaccinated, you’re still a danger, and you’re still in danger as well, so get vaccinated.”
A growing body of research indicates that the risk of spreading the virus is far lower outdoors than indoors. Viral particles disperse quickly outdoors, experts say, meaning brief encounters with a passing walker or jogger pose very little risk of transmission.
“That biker who whizzes by without a mask poses no danger to us, at least from a respiratory virus perspective,” Dr. Paul Sax, an infectious disease specialist at Brigham and Women’s Hospital, wrote in a blog post for The New England Journal of Medicine.
A recent systematic review of studies that examined the transmission of the coronavirus and other respiratory viruses among unvaccinated individuals concluded that fewer than 10 percent of infections occurred outdoors and that the odds for indoor transmission were 18.7 times higher than outdoors. (The odds of superspreading events were 33 times higher indoors.)
But the paper’s author said that the low odds of transmission outdoors could simply reflect the fact that people had spent little time outside. In cases where transmission occurred outdoors, there was often also prolonged or frequent contact with another individual or a group of people, or an indoor component to an outdoor gathering, said Dr. Nooshin Razani, an associate professor of epidemiology and biostatistics at the University of California, San Francisco.
“It does happen: You can get infected outdoors,” she said. “It usually has to do with how long you’re with someone and how often you see them, and if you’re wearing a mask and if you’re close to each other.”
The C.D.C. currently recommends that vaccinated people should wear masks and maintain six feet of distance from others in public, including while taking public transportation such as buses, trains or planes and while in transportation hubs. It also recommends they continue to avoid crowds, large gatherings and poorly ventilated spaces.
Kevin Draper contributed reporting.