The Centers for Disease Control and Prevention (CDC) is expected to update its guidance Tuesday and once again recommend that fully vaccinated Americans wear masks indoors in some cases, citing the highly contagious delta variant.

The CDC is expected to recommend that people who are vaccinated should wear masks indoors in parts of the U.S. where COVID-19 is surging, a federal official told The Associated Press. Sources told CNN that the CDC will recommend that people in areas with substantial or high community transmission should wear masks indoors.

The news was first reported by the New York Times and confirmed by the Washington Post and NBC News. The CDC is expected to detail its updated guidance at a briefing later Tuesday afternoon.

The updated guidance would reverse the decision that the CDC made in May to loosen mask restrictions for fully vaccinated Americans, citing falling cases and a rise in inoculations nationwide.

But health officials are sounding the alarm nationwide amid a surge in COVID-19 cases in areas with low vaccination rates and reports of rising breakthrough cases.

"We’re going in the wrong direction,” Dr. Anthony Fauci, the nation's top infectious disease expert, told CNN on Sunday.

This is a developing story. Check back later for further updates.