The U.S. Centers for Disease Control and Prevention (CDC) is expected to recommend that vaccinated people in parts of the country wear masks while indoors, reversing a decision it made two months ago.
Federal officials with knowledge of the decision told news agencies the CDC is expected to make the announcement later Tuesday, based on surging numbers of new cases in regions with low vaccination rates.
The rising caseload is driven by the highly contagious delta variant of the coronavirus that causes COVID-19.
There has also been a rise in cases of so-called breakthrough infections among fully vaccinated people, suggesting the delta variant may be able to cause such infections more often than previous strains of the virus.
Health officials say vaccines remain effective against the worst outcomes of infection with the virus, including those involving the delta variant.
In televised interviews Sunday, White House medical advisor and top U.S. infectious disease expert Anthony Fauci said the mask guidelines were under review, as new infections in areas with low vaccination rates have been surging. The CDC says 30 states have less than half their residents fully vaccinated.
In May, the CDC said fully vaccinated people no longer would be required to wear masks or maintain social distancing of six feet from other people. The agency still suggested people remain masked on public transportation and at crowded outdoor events.
For months, COVID-19 cases, deaths and hospitalizations in the U.S. fell steadily, but those trends reversed over the past two months as the delta variant of the coronavirus began to spread.
The New York Times reports several cities and towns have restored indoor masking rules in recent weeks, including St. Louis, Missouri, Savannah, Georgia and Provincetown, Massachusetts.