A medical assistant administers a coronavirus test to a person at Sameday Testing in Los Angeles this week.

People enjoy an outdoor art exhibition in downtown Los Angeles in early July. Los Angeles County public health authorities are now urging unvaccinated and vaccinated people alike to wear face coverings in public indoor spaces because of the growing threat posed by the more contagious delta variant of the coronavirus.
Tourists crowd into the Midway Geyser Basin at Yellowstone National Park in Wyoming on July 14. Yellowstone is one of many national parks seeing record numbers of visitors this summer, even as coronavirus cases are rising in many states.