The United States is one of the only countries worldwide to allow fully vaccinated people to go without masks while the rate of COVID-19 infections remains relatively high.
Other countries with higher vaccination rates and lower infection rates still require masks indoors.
Guidance released last week from the U.S. Centers for Disease Control and Prevention lifted restrictions for vaccinated people once two weeks had passed since their last shot.
"Anyone who has been fully vaccinated can participate in indoor and outdoor activities large or small without wearing a mask or physical distancing," CDC Director Rochelle Walensky told reporters Thursday.
Masks are still required indoors in Israel, where more than 60% of the population has received at least one vaccine dose and infection rates per 100,000 people are in the single digits.
"While I can say (an end to the mandate on masks indoors) is on the way, I still cannot specify time frames," coronavirus czar Nachman Ash told Israeli news site ynetnews.com.
In Britain and Italy, lockdown restrictions are easing, but indoor mask requirements remain.
Australia and New Zealand do not have mask mandates. But they also have almost no COVID-19 cases.
Walensky said the CDC made the decision because U.S. cases had fallen by one-third in the past two weeks. She noted research showing that the vaccines are safe and effective at preventing infection and transmission of the virus. And the vaccines are widely available, including, as of last week, to adolescents 12 to 15 years old.
Less than half the population has received at least one shot, however, and new infections still average more than 30,000 per day.
The CDC's action drew mixed reactions from public health experts outside the United States.
"From a biologic standpoint, the move makes sense," said McMaster University infectious disease physician Zain Chagla. "We know that these vaccines significantly reduce the risk of death and disability from COVID-19 (and) reduce transmission."
However, he added, "there's no verification system." If unvaccinated people decide they do not want to wear masks, there is little that can be done to keep them out of public places.
That puts at risk those who are not fully vaccinated or eligible to be vaccinated yet, including children.
"The U.S. is really charting their own seas by focusing this on the individual rather than the population," Chagla added.
Other countries have focused more on metrics such as new cases, hospital capacity and vaccination rates to guide decisions on whether to loosen or tighten restrictions.
Walensky agreed that local leaders should look to those measures to make their decisions.
"There are some places that have more disease than others and less vaccination rates than others," she said on Fox News Sunday. Officials "should be looking within those communities before removing mask policies."
Not all states are following those recommendations. More than half have already lifted mask mandates, including some with high transmission rates.
Masks are still required on planes, trains and buses; in hospitals; and in states, cities and businesses that require them.
Critics have said this patchwork approach will make things harder for people in public-facing jobs.
"Workers are still forced to play mask police for shoppers who are unvaccinated and refuse to follow local COVID safety measures. Are they now supposed to become the vaccination police?" said Marc Perrone, president of the United Food and Commercial Workers, a union representing supermarket, retail and other essential workers.
Many warned that the messaging is too complicated.
"The average person will not try to take stock of what the data means. They want a simple message," said Northumbria University infectious disease expert Sterghios Moschos. "The simple message here is that the virus is still circulating, so we need to do everything we can to suppress this circulation as much as possible."
That means keeping masks on.
Walensky said the CDC does not disagree.
"There's no need for everybody to start ripping off their masks," she said on NBC's Meet the Press.
"What we're saying is, now this is safe," she said. "Work at your own speed. Work with your own family and your own businesses to remove them when necessary."