White House Chief Medical Advisor Dr. Anthony Fauci said fully vaccinated people should consider wearing masks indoors as a precautionary measure against the highly contagious Delta variant in the U.S.

“If you want to go the extra mile of safety even though you’re vaccinated when you’re indoors, particularly in crowded places, you might want to consider wearing a mask,” Fauci told CNBC on Wednesday.

High vaccination rates had raised hopes that the long-awaited pre-pandemic life was back to normal, but COVID-19 cases have been on the rise with the new Delta variant. Now, Americans are starting to see a summer with new mask recommendations. 

​​“It’s suggested that you wear a mask when you are indoors in a situation where you have a level of dynamics of virus in the community that’s high,” Fauci said.

Several places from California to Massachusetts have already been advising residents to wear masks in public indoor settings, regardless of their vaccination status. 

Much like Dr. Fauci’s recommendation on Wednesday, these new state measures come as a preemptive step to avoid strict pandemic guidelines. 

Earlier in May, the Centers for Disease Control and Prevention released an updated COVID guidance saying fully vaccinated people did not have to wear a mask or social distance. These guidelines are now changing as more information regarding vaccine efficacy against the delta variant is released and vaccination rates wane. 

CDC director Dr. Rochelle Walensky told lawmakers at a Senate hearing Tuesday that the agency is actively reviewing its mask and other public health guidelines as the virus and pandemic evolve.

“A lot has changed since May,” Walensky testified. “We now have a variant circulating in this country that at the time was 3% (of new cases) and is now 83% and much more transmissible.”

COVID infections are on the rise again in the U.S after they had been declining for a few months. New cases jumped by 55% since last week to an average of 37,000 new cases per day over the last seven days, according to a CNBC analysis.

In most states, more than 97 percent of new Covid-related hospitalizations are among those who are unvaccinated.

Currently, 10 states and territories have statewide mask-wearing orders, including California, Connecticut, Washington D.C., Hawaii, Illinois, Nevada, New Mexico, New York, Puerto Rico and Washington.