In this May 23, 2021, file photo, pedestrians wearing masks out of concern for the coronavirus walk in the Harvard Square neighborhood of Cambridge, Massachusetts. Credit: Steven Senne / AP

WASHINGTON — The director of the National Institutes of Health said federal guidance urging vaccinated people to wear masks indoors in communities of high COVID-19 spread is aimed at mostly protecting the unvaccinated and immunocompromised.

Dr. Francis Collins told CNN’s “State of the Union” that mask mandates can help as virus infections spike higher in parts of the U.S. because studies show vaccinated people can spread the virus to others.

But he stressed Sunday that masks are no substitute for getting a shot, which work “extremely well” and reduce a person’s risk of serious illness and hospitalization by “25-fold,” including the delta variant.

Collins warned that right now the virus is “having a pretty big party in the middle of the country” but the silver lining is that more people are now getting the shot.

He said businesses may need to step up to require vaccinations, and that a case can be made for airlines to consider them as well for passengers. In recent days, Disney and Walmart have asked their employees to be vaccinated.