It started in the air. After a federal judge struck down mask requirements on planes, pilots and passengers tore off their masks with joy.

The pilot for Delta was halfway between the two cities when the announcement came. Brooke Tansley, who was flying with two children too young to be vaccine free, said she felt scared as the passengers around her slipped off their masks.

A judge's determination that the federal government had overstepped its boundaries caused a domino effect across the country. The unexpected ruling by a judge in Florida instantly changed travel for millions and caused political divisions over where to hide from the virus.

The country's pandemic rules are a patchwork. Many subways, buses and ride-share services had mask requirements removed. The rules were still in place in several major cities. Subway riders in New York City are still required to wear facial coverings, but New Jersey transit riders are allowed to take theirs off. In Philadelphia, people were allowed to go without masks on the trains and buses.

President Biden told reporters in New Hampshire that people should continue to wear masks.

ImageMoynihan Train Hall in Manhattan. Although Amtrak no longer requires masks, they must be worn on New York subways.
Moynihan Train Hall in Manhattan. Although Amtrak no longer requires masks, they must be worn on New York subways.Credit...Hilary Swift for The New York Times
Moynihan Train Hall in Manhattan. Although Amtrak no longer requires masks, they must be worn on New York subways.

Many domestic airlines made masks optional after the Transportation Security Administration said it wouldn't enforce mandates, while some European carriers kept mask rules in place.

Washington's messages added to the uncertainty. The administration's Covid-19 response coordinator, Dr. Ashish K. Jha, said he would continue wearing a mask on flights despite the judge's ruling. The Biden administration said on Tuesday that it would appeal the ruling if the Centers for Disease Control and Prevention decided to extend the masking measure on public transportation. The mandate was extended into early May this month, before it was set to expire.

In most aspects of American life, masks are no longer required. airports, public transportation, and medical facilities were the largest exceptions. Millions of Americans were affected by the decision on Tuesday.

In Las Vegas, passengers and flight crews walked past security checkpoint signs that read "Masks required!" and "At one ticket counter, an agent checking passengers' luggage wore DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch DropCatch

She said she was relieved to be able to fly back to Maryland. I have already been shot. It doesn't make sense.

Many public health officials warned that new infections were edging back up.

Older Americans, people with compromised immune systems, parents with young children and low-income workers who rely on public transportation were worried that they would now be at even greater risk with every bus ride or plane trip.

Catherine Muskin is a lawyer in Ithaca, N.Y. and a mother of two young children. She said the end of airline mask mandates made it impossible for her and her husband to go to Florida for a vacation. We are now the exception.

ImageHartsfield-Jackson Atlanta International Airport. Many domestic airlines quickly made masks optional after the Transportation Security Administration said it would stop enforcing mandates.
Hartsfield-Jackson Atlanta International Airport. Many domestic airlines quickly made masks optional after the Transportation Security Administration said it would stop enforcing mandates.Credit...Dustin Chambers for The New York Times
Hartsfield-Jackson Atlanta International Airport. Many domestic airlines quickly made masks optional after the Transportation Security Administration said it would stop enforcing mandates.

The new mask rules arrived. Less Americans are hospitalized with Covid-19 than at any point since reliable data collection began in spring of 2020 and case reports have plummeted since the Omicron variant first swept over the country around New Year's. Deaths have fallen rapidly in recent weeks, from more than 2,600 reported each day in early February to less than 500 a day over the past week.

There were many reasons for concern about the weeks ahead.

New case reports are low but rising, and are believed to be a significant undercount because of the popularity of at- home tests. Two new versions of Omicron, both of which evolved from the subvariant BA.2, have been spreading rapidly in New York.

On the East Coast and around the Great Lakes there has been a steep increase in cases. Over the past two weeks, new case reports have more than doubled in Michigan, New Hampshire and Pennsylvania.

Several public health experts said that the judge's ruling was more alarming because of the increases.

If I were impolite, I would say kind of stupid. She said that the ruling was not in line with public health principles.

Dr. Robert Wachter, who chairs the department of medicine at the University of California, San Francisco, has recently said it is time to lift mask requirements. He asked the Biden administration to challenge the ruling.

If this becomes a precedent, that a judge can overrule government and C.D.C. experts, that puts us in a problematic place for the next surge, the next pandemic, bioterrorism or who knows.

ImageIn Philadelphia, where officials had reinstituted an indoor mask requirement this week, people were allowed to go maskless on trains and buses.
In Philadelphia, where officials had reinstituted an indoor mask requirement this week, people were allowed to go maskless on trains and buses.Credit...Rachel Wisniewski for The New York Times
In Philadelphia, where officials had reinstituted an indoor mask requirement this week, people were allowed to go maskless on trains and buses.

For some, the decision meant relief.

It feels good to get on a plane and not have to worry about having to pull it up.

The ruling deepened divisions about how to approach the epidemic and what role government rules should play. The change felt premature to Candice Bailey, who works in education. She wore a mask at the New Orleans airport to catch a plane back to North Carolina.

There is a lot more information that needs to be gathered before you can make a determination.

Dr. Rebecca Lee Smith, an epidemiologist at the University of Illinois, said her family had been weighing whether to drive or fly for a vacation this summer, but has now decided on driving because she has a child who is not old enough for a vaccine.

She said that the ruling on masks was unfortunate because some people at higher risk of severe illness might have no choice but to use public transportation.

Dr. Smith said that we need to protect the people who have to use these, who may not have other protections.

According to a Harris Poll conducted this month, at least 60 percent of adults supported keeping a mandate. Some travelers said they didn't know what to think.

At the check-in counter at the Atlanta airport, Juston Stills was not wearing a mask, but he was going to put one on before his flight to Fort Lauderdale, Fla. Mr. Stills said that he has been considering whether to wear a mask for the past few months. He doesn't wear a mask in small groups. He wears one at his daughter's school and on public transit.

ImageThe ruling deepened divisions about how to approach the pandemic, and about what role government rules should play.
The ruling deepened divisions about how to approach the pandemic, and about what role government rules should play.Credit...Hilary Swift for The New York Times
The ruling deepened divisions about how to approach the pandemic, and about what role government rules should play.

Since we have no clear direction from our governors, the president, and the C.D.C., I have been going with the vibes, he said.

Airport operators and transit systems were left to make their own decisions in the absence of a national mandate.

The Port Authority of New York and New Jersey, which operates the three major airports in the New York metropolitan area as well as interstate buses and bus terminals, said it would follow the local guidance in each state. There were mask mandates at their airports in New York, Kennedy International Airport and La Guardia Airport, but not at Newark Liberty International Airport in New Jersey.

New York and San Francisco have large public transit systems that kept mask rules in place. In Milwaukee, officials said on Tuesday that masks would be optional for bus riders, before changing their minds and reverting to a mandate for the evening rush hour. In Boston, Atlanta, Washington, and Philadelphia, riders were allowed to drop their masks.

There were signs that did not keep up with the rules. Most passengers and employees did not wear masks at the airport in Grand Rapids, Mich., on Tuesday.

The airline customer service agent in Grand Rapids said that she doesn't feel uncomfortable at the counter because she has been vaccinations.

It was a big change after two years.

There was confusion on all sides of the debate.

Joseph Suaznabar had just arrived barefaced at the airport in Chicago. He had to put his face covering back on when he went to board the train that would take him to the city.

I try to do what I am told, but it is hard to know what to do anymore.

The train mandates in Chicago had been lifted by Tuesday night.

Reporting was done by Matt Berg, Robert Chiarito, Niraj Chokshi, Heather Murphy, Tariro Mzezewa, Sharon Otterman, Roni Caryn Rabin, and Katie Rogers.