他人とある程度離れていれば、外ではマスクはかなずしも必要ではないのでは、と。

 Do we still need to wear a mask outdoors?

By Keri Enriquez, CNN

Updated 2131 GMT (0531 HKT) April 22, 2021

Nooshin Razani, one of the authors and an associate professor of epidemiology and biostatistics at the University of California, San Francisco, told Slate the true number of instances of outdoor transmission was "probably lower" than 10%.

Current guidance from the US Centers for Disease Control and Prevention makes it clear masks might not be needed outside. "Masks may not be necessary when you are outside by yourself away from others, or with people who live in your household," it says. The CDC does not say anything specific for vaccinated people.

"If you're unvaccinated and constantly passing by people close enough that you can reach out and touch them, then you should wear a mask," Marr told CNN.

Vaccinated or not, an important factor in deciding to unmask outdoors is the levels of transmission and positivity in your area, Gupta said.

"The real question you need to try to answer is, what is the likelihood I'm going to breathe in someone else's air? That's basically it. The number of people, type of setting and what is the overall viral spread in their community," Gupta said.

　屋外での感染は全体の１０％ で、アメリカの疾病対策予防センターは、他人からある程度距離があれば、マスクはかなずしも着用する必要ないのではないか、と。もっとも、ワクチン接種しておらず、手の届く範囲に常に人がいるような場合は、マスクをすべきだ、と。要するに、その地域の感染者、感染率がどれくらいで、どのような場所にいて、他人の呼気を吸い込む可能性はどれくらいか、による、と。