Masks are back, and, this time, they’re not just for COVID-19. A "tripledemic” of the coronavirus, influenza and respiratory syncytial virus, known as RSV, sweeping through the United States has prompted several cities and counties, including New York City and Los Angeles County, to encourage people to wear a mask in indoor public spaces once again.

Nationwide, COVID-19 case rates and hospitalizations have spiked by 56% and 24%, respectively, over the past two weeks. The Centers for Disease Control and Prevention estimates that there have already been 13 million illnesses and 7,300 deaths from flu this season, and those numbers are expected to rise in the coming months. (Over the past decade, annual flu deaths have ranged from 12,000 to 52,000 people, with the peak in January and February.) And while RSV finally appears to be on the decline, infection rates are still high across much of the country.

The CDC officially advises wearing a mask on a county-by-county basis depending on community COVID-19 levels, which take into account virus-related hospital admissions, bed capacity and case rates. However, in an interview with NPR last week, Dr. Rochelle Walensky, the CDC director, said, "You don’t need to wait for CDC’s recommendation, certainly, to wear a mask.”