President Joe Biden’s top health adviser said Thursday that people who have been fully vaccinated against the coronavirus don’t have to wear a mask outside.

“It would be a very unusual situation if you were going into a completely crowded situation where people are essentially falling all over each other,” Dr. Anthony Fauci told CBS “This Morning.” “Then you wear a mask. But any other time, if you are vaccinated and you are outside, put aside your mask, you don’t have to wear it.”

Late last month, the Atlanta-based Centers for Disease Control and Prevention updated its guidelines to also say Americans who have been fully vaccinated don’t need to wear masks outdoors.

The CDC said masks are no longer required for such activities as outdoor walking, running, hiking or biking; small outdoor gatherings with fully vaccinated family and friends; small outdoor gatherings with a mixture of fully vaccinated and unvaccinated people; and dining at outdoor restaurants with friends from other households.

Fully vaccinated people can also attend “a crowded, outdoor event, like a live performance, parade, or sports event,” as long as they remain masked, according to the CDC.

COVID-19 deaths in the United States have tumbled to an average of about 600 per day — the lowest level in 10 months — with the number of lives lost dropping to single digits in well over half the states and, on some days, hitting zero.

Confirmed infections have fallen to about 38,000 per day on average, their lowest mark since mid-September. While that is still cause for concern, reported cases have plummeted 85% from a daily peak of more than a quarter-million in early January.

The last time U.S. deaths from the pandemic were this low was in early July of last year. The number of people with COVID-19 who died topped out in mid-January at an average of more than 3,400 a day, just a month into the biggest vaccination drive in the nation’s history.

About 45% of the nation’s adults are fully vaccinated, and nearly 59% have received at least one dose, according to the CDC. This week, Pfizer’s vaccine won emergency-use authorization for 12- to 15-year-olds, a move that could make it easier to reopen the nation’s schools.

Several states, including Wyoming, Vermont, Alaska and Hawaii, were averaging fewer than one COVID-19 death per day over the past week, according to data through Tuesday from Johns Hopkins.

And even among the five states with the highest daily deaths — Michigan with an average of 65.4, Florida with 61.7, California with 48, Texas with 44 and New York with 39.3 — all but Florida’s number were going down.

California, the epicenter of the U.S. outbreak over the winter, logged 1,231 new confirmed cases Wednesday, down from a peak of 40,000. Los Angeles County reported 18 deaths Tuesday, versus more than 200 a day in January.

Vermont, which at nearly 63% leads the country in the share of its population that has received at least one vaccine dose, has gone nearly a week without reporting a COVID-19 death.

The improvement hasn’t been as dramatic everywhere. Michigan, which for weeks has reported the nation’s worst infection rate, is only now starting to see a decline in mortality. But over the past two weeks, cases in the state plunged from a daily average of almost 4,860 to about 2,680 on Monday.

The Associated Press contributed to this report.