Mask mandates were extended for U.S. transit, but dropped in many other settings: The week in Covid news.

In an aggressive step toward normalcy, public school students in New York City returned to mask-optional classrooms on Monday for the first time since the start of the pandemic.

In Puerto Rico, the governor lifted the territory’s mask mandate for most places, as one of the last holdouts in the United States to ease Covid-19 restrictions. Hawaii followed suit on Tuesday, becoming the 50th and final state to announce that it would drop its universal indoor mask mandate as the nation tries to move on from the once ferocious Omicron wave.

But removing masks is still contested in some places. The Chicago teachers’ union vowed to fight plans to lift a mask mandate in the nation’s third-largest school district and one young New Yorker told reporters he felt unsafe without a mask on at school.

On Thursday, the Transportation Security Administration announced it will extend its mask mandate for airplanes and other public transportation through mid-April, as the Centers for Disease Control and Prevention said it would work with federal agencies to revise mask policies.

The requirement will remain in place at least through April 18. Under the T.S.A.’s rule, passengers on airplanes, buses and trains and at airports and transit stations must wear masks.

But the relatively short extension signaled that the federal government may be preparing to wind down the requirement, at least in some places. The C.D.C. was consulting other federal agencies to determine when masks should be required on public transit, taking into account case counts and the risks of new variants, among other factors.

Here’s what else happened this week:

• The once intense Omicron wave that has retreated in much of the world is flaring up in parts of East and Southeast Asia. Some countries are enduring their worst waves of the pandemic, the World Health Organization noted this week.

• Ukraine’s health care system is still grappling with the coronavirus pandemic, even as it tries to cope with the severe effects of an invasion that has sown destruction and dislocation in the country, the W.H.O.’s regional director for Europe said on Tuesday. Ukraine reported 731 Covid deaths to the organization last week, a figure that probably underestimates the true toll.

• Thirteen Democratic state governors wrote to the Health and Human Services secretary, Xavier Becerra, this week, urging him to extend the country’s public health emergency declaration for at least another three months beyond its scheduled expiration in April. The governors said that they need much more time to prepare.

• Novak Djokovic, one of the world’s most prominent sports stars to hold out against getting a coronavirus vaccination, said Wednesday that he can’t enter the United States because he is unvaccinated and won’t participate in the Indian Wells tennis tournament that began this week and runs through next weekend in Southern California.

• Officials in Ontario, Canada, said on Wednesday that the province was dropping its universal mask mandate, weeks after truckers paralyzed Ottawa, the country’s capital, during protests over coronavirus restrictions.