Under a new health order, San Franciscans no longer need to wear a mask while doing outdoor activities like walking or biking when they’re alone or with members of their household. Unvaccinated people should wear a mask if social distancing can’t be maintained. Fully vaccinated people can almost entirely forgo masks outdoors, with some specific exceptions. Dr. Susan Philip, San Francisco's health officer, explains the details of the new order and how these decisions are made.