Riding the bus is a risk for Joanne Daniels-Finegold, but the 69-year-old wheelchair user with asthma, kidney problems and a blood-clotting disorder has no other way to get to the grocery store, her doctor’s office or a weekend job greeting people at a farmers market in suburban Boston.

“If I have to go somewhere, I have no choice,” she said.

Like many medically vulnerable people, Daniels-Finegold now must take that risk without the protection of a mandatory mask policy after a federal judge in Florida voided a nationwide requirement on planes, trains, buses and other modes of public transportation. Over the past week, mask mandates have been revoked on transit systems across the United States, including in places like Boston and D.C. that recently have seen rising case numbers and elevated levels of community spread.

The relaxed rules have some people rethinking the safety of their daily commute – especially those at heightened risk of severe COVID symptoms because they are over 65, have an underlying health condition like asthma or are immunocompromised. Those same issues are top of mind for many bus operators, who endured widespread outbreaks during the omicron surge and had colleagues die of the disease.

At the start of the pandemic more than two years ago, transit systems put protections in place to keep bus operators safe. By late March 2020, Washington, D.C.’s Metro – the nation’s third-largest transit system – began requiring bus riders to board from rear doors while forgoing fares so the front door and first few rows of seats could be blocked off, creating a buffer between drivers and passengers. Transit agencies across the country adopted similar procedures.

Metro resumed front-door boarding in January 2021. By then, transit officials said, protective shields enclosing bus operators were installed on all Metrobuses, buses were regularly disinfected and riders were still required to wear masks.

The highly contagious omicron variant decimated transit agencies late last year, pushing more Metro employees out of work than at any time during the pandemic while exacerbating a driver shortage plaguing the industry.

The coronavirus is spread by breathing in tiny particles of virus in the air, and studies have shown it can be spread during bus rides. In the early days of the pandemic, a study of a large outbreak on a bus in China showed the virus spread easily among the unmasked passengers. The 68 passengers were in the same vehicle for a 100-minute, round-trip ride without masks. Twenty-four tested positive after the journey.

But not all buses are created equally. A 2020 study by researchers at California State University in Fresno found that virus particles can spread through a bus within seconds of being released into the air, but mitigation efforts to improve air circulation can significantly reduce the risk. Heating, cooling, positive pressure and other efforts to filter and replace the air on a bus greatly reduce the risk of exposure, the study found.

In Wisconsin, for instance, Green Bay Metro was among the first bus systems to install air-purification systems on its entire fleet about a year and a half ago, paid for with the help of $6.4 million that the agency received from federal coronavirus relief aid. The system, which uses UV technology, has proven to be effective on most viruses, including covid, transit officials said. The goal, they said, was to protect riders with limited options.

Even with the advanced system, Green Bay Metro officials urged people to continue wearing masks, which enhance protection as the first line of defense against transmission, the Cal State researchers concluded.

Some high-risk passengers face tough decisions when balancing the need to get around against the potential danger of exposure to the virus.

Dania Douglas, 45, has lived in the District of Columbia for 22 years and said she has relied on public transit. With the mask mandate gone, Douglas said she is rethinking public transit, especially during times when her immune system is suppressed by steroids she takes to treat an autoimmune disorder.

“I feel there is very little I can do,” she said. “I leave home now occasionally for medical appointments or to go to CVS to get prescriptions. How do I get there safely?”

D.C. resident Bethany Lilly, 36, has mostly avoided public transit because she worried her asthma would put her at heightened risk for severe illness if she caught the virus. Despite her efforts, Lilly could not escape the omicron variant this winter. She tested positive Dec. 31 and spent two weeks fighting off symptoms and falling asleep on the couch by 3 p.m. most days. Although the coughing and sneezing waned, Lilly’s extreme fatigue lingered for months.

Lilly said her doctor told her to cut back on the bike rides to give her body, especially her lungs, a chance to heal. Since then, she has been taking the bus and subway to get around, though she said she might stop since masks are optional.

“Getting (COVID) has made me a much more cautious commuter,” Lilly said. “I am already dealing with all of these complications and I don’t want to add any more risk.”

While omicron has faded, coronavirus case counts are pointing up. The rate of infections prompted Los Angeles County on Thursday to reinstitute a mask order for transit. Transit systems in New York also remain under a state order requiring masks.

But most other agencies have dropped their mandate, including Metro and the New Orleans Regional Transit Authority. Those agencies and the New York Metropolitan Transportation Authority were the only major transit systems in the country that required employees to be vaccinated.

New Orleans, where COVID cases and hospitalizations are on the rise, has lost at least four transit employees to the virus, said Kory Dupree, president of the Amalgamated Transit Union Local 1560, which represents workers at the transit agency.

Some bus operators say they wish the mask mandate had remained in place, especially with tourist season approaching, Dupree said. For the first time since the pandemic, New Orleans will host the New Orleans Jazz & Heritage Festival, the 52-year-old music festival that stretches over two weekends, drawing more than 400,000 – roughly equal to the city’s population.

“We have all these different festivals about to come into play, and one is the JazzFest, which brings you not just folks from all over the country but all over the world,” Dupree said. “I told my members, just make sure you play the safe card even though it’s lifted for our riders, just take precautions and still wear your mask.”

Elsewhere, many union officials view the lifting of the mandate as a mixed blessing. John Costa, international president of the Amalgamated Transit Union, North America’s largest transportation worker guild, noted in a statement that “the CDC still recommends wearing masks on public transit.”

He said the mask requirements were a source of tension between noncomplying riders, other passengers and bus drivers who felt obligated to enforce the mandate. That often made them targets for violent attacks, which increased against transit workers during the pandemic.

“We can also not ignore the fact that the mask mandate required our members to deal with unruly passengers who refused to comply with the mandate as we continue to urge transit agencies to protect our members on the job,” Costa said.

The American Public Transportation Association said in a statement that it did not support the Biden administration’s appeal of the Florida ruling that struck down the federal mask order. The nonprofit, which represents 1,500 public and private transit agencies, said in a statement that “reimposing a federal mask mandate would cause considerable confusion among riders and increase the growing enforcement challenges faced by public transit agencies today.”