A mask mandate has gone into effect for all 11 of New York City's public hospitals after an increase in COVID-19, flu and respiratory syncytial virus cases.

The mask requirement also applies for all health clinics and nursing homes run by NYC Health + Hospitals.

Dr. Lipi Roy, an internal medicine physician, said Tuesday that "masks can really prevent the transmission of the virus, all 3 of the viruses, RSV, influenza and COVID-19."

The Centers for Disease Control and Prevention recently warned that respiratory illnesses are on the rise across the country. Just before Christmas, national COVID-19 hospitalizations jumped 17% in one week.

"I think that's a major reason why we're seeing this rise in not only cases, but also hospitalizations. Because we've just had Thanksgiving, Christmas, New Year's, so a lot of people are gathering from all over the country," Roy told NY1.

The mask mandate for the city's public hospitals went into effect just after Christmas. A spokesperson for NYC Health + Hospitals told NY1 that the mask requirement is meant to protect both patients and health care providers.