Since the beginning of President Biden’s term in January 2021, a federal mask mandate for public transportation has been in place, affecting everything from local bus routes to transcontinental flights. On Monday, the federal mask mandate for public transportation was struck down by Judge Kathryn Kimball Mizelle. While the Justice Department has appealed this ruling by Mizelle — who, at the time of her appointment by Donald Trump in 2020, was declared “not qualified” by the American Bar Association — it hasn’t sought or received a stay, meaning the mask mandate will not be in effect while the decision is appealed.

The CDC still recommends people wear masks on public transportation, but ultimately it’s now up to airlines, transit authorities, and ride-hailing companies to decide whether to require masking — and it’s up to individuals to figure out, in the absence of those requirements, what they should do to protect themselves and others.

“I would certainly still wear masks on public transit,” said Katelyn Jetelina, an assistant professor of epidemiology at the University of Texas Health Science Center at Houston and the author of the Your Local Epidemiologist newsletter. “Not just for individual-level risks, but also to help those that are much higher risk, and for those vulnerable pockets in the community.”

Here’s why you should continue to mask on transit — even in the absence of a mandate — along with some expert tips for protecting yourself and others when you’re commuting or traveling.

The science still supports masking on transportation

It’s important to know that Health Freedom Defense Fund v. Biden, the case that led to the ruling striking down the travel mask mandate, was strictly about whether or not the federal government had the authority to implement the mandate; it was not about whether masking on transit is currently legitimate or useful from a public health standpoint.

But the idea that the CDC doesn’t have this authority is also bogus. As my colleague Ian Millhiser wrote on Tuesday, Mizelle’s opinion in this case “is so poorly reasoned that it is difficult not to suspect that it was written in bad faith.” He continues: “The most likely reading of her opinion is that she simply disagreed with the Biden administration’s masking policy, and concocted a justification for striking it down.”

The fact that the mandate was struck down is not a sign that masking on transit or planes lacks scientific merit. The evidence shows that masks work and are an important Covid-19 mitigation measure when indoors in public.

“We know that Covid-19 is airborne and spreads via an aerosol that builds up in enclosed spaces,” said Matthew Cortland, a senior fellow working on disability and health care at the think tank Data for Progress. “The less Covid-19 that’s in the air around us, the safer we are. Masks reduce the amount of that infectious aerosol. The science is very clear.”

While it’s true that cases have dropped dramatically across the US since the winter omicron surge, the numbers are starting to go back up. According to the New York Times, “Cases have increased in a majority of states and territories during the past two weeks, but the inclines are sharpest in the Northeast and Midwest. In Washington, DC, Michigan, and New Hampshire, cases have more than doubled since the start of the month.” This may also be an undercount, given the widespread use of at-home antigen tests whose results are not officially recorded.

Hospitalizations thankfully remain relatively low at present, but there are still plenty of good reasons to want to avoid infection, and to actively avoid passing the virus to others. “Every one of the 462 deaths caused by Covid-19 is a tragedy,” Cortland said, referring to the deaths on April 19, the day of our interview. “But preventing tragic deaths is not the only reason to prevent the spread of Covid-19. Even in people who are fully up to date on their vaccinations, Covid-19 can still cause long-term, serious health complications. Yes, long Covid, but Covid-19 also raises the risk of diabetes, abnormal heart rhythms, heart muscle inflammation, blood clots, strokes, myocardial infarction, and heart failure.”

Beyond this, the more the virus spreads, the more likely we are to get new variants, which have the ability to prolong this pandemic even more.

If you want to protect yourself, one-way masking definitely helps

One-way masking, or wearing a mask to protect yourself from the people around you who are unmasked, is fairly effective. “One-way masking helps a lot,” Jetelina said. “This is especially true when you have a well-filtered, well-fit mask like an N95, KN95, or KN94. They do a really great job at protecting the wearer. I feel very confident when I’m wearing one.”

Cortland also emphasized the importance of wearing high-quality and well-fitting masks indoors, and suggested that people who are relying on one-way masking to stay safe should perform a seal check (a few tutorials here, here, and here) to ensure their mask is as protective as it can possibly be. “To be clear, it is not a replacement for a professional seal check,” Cortland said. “It is better than nothing, which is what the CDC and the rest of the federal government is offering.”

But keep in mind that one-way masking is not a panacea, especially when community transmission is high. Emergency medicine physician Jeremy Faust recently did statistical modeling to determine when a KN95 or N95 would be enough to protect a severely immunocompromised person if they were the only person wearing one. Faust determined that once a community surpasses a weekly average of 50 cases per 100,000 people, one-way masking becomes unlikely to be enough to ensure very strong protection. While a lot of factors are at play here, including an individual’s risk status, vaccine status, and mask fit, it’s helpful to know that one-way masking can only take us so far. The more people who wear masks in public spaces, the better.

Your mask also protects everyone who can’t opt out of using transit

Even if you feel okay about your personal risk, wearing a mask in public is key to protecting others, including unvaccinated kids and the immunocompromised. People who are worried about getting Covid-19 cannot, and should not have to, stay home if they aren’t comfortable entering mask-optional public spaces. High-risk people (just like lower-risk people!) need to be able to access essential public spaces — hospitals, pharmacies, grocery stores, and, yes, public transportation — to meet their basic needs and earn a living.

“CDC’s mask requirement applied to airplanes; it also applied to subways, trains, buses, ferries, taxis, and ride-shares,” Cortland said. And a lot of people in the US are reliant on those forms of transportation, they pointed out; in 2019, Americans took 9.9 billion trips on public transit and 14.3 percent of workers commuted to work by public transportation in the Northeast.

“We use the subway to get to the grocery store, the bus to get to the pharmacy, ride-shares to get to work,” they continued. “To exclude tens and tens of millions of Americans from public transit — by making these conveyances unsafe — is not good for public health, it is not good for our economy, it is not good for our country.”

Jetelina said that she’s particularly concerned with people not wearing masks on trains and buses, which have terrible ventilation systems compared to planes. “My biggest fear with this is that there are going to be health equity concerns linked with this, and communities are going to be disproportionately impacted,” she said. “And with that, they will have even more mortality and morbidity, so it becomes this very dangerous revolving door.”

If you’re traveling by plane, ventilation alone won’t keep you (or others) safe

“Filtration and ventilation are incredibly useful on airplanes,” Jetelina said. “And they’re very powerful, especially if we compare it to other spaces. But they’re not perfect.”

Jetelina said one problem is that a plane’s ventilation and filtration systems aren’t actually on for the entirety of a trip — for example, they often aren’t running when the plane is sitting at the gate. This, coupled with the fact that airports are often crowded and don’t have the same highly effective ventilation system that a plane does, could mean significant time spent without these layers of protection. At minimum, you should wear a high-quality, well-fitting mask when you’re taking transit to the airport, in the airport, boarding the plane, taxiing on the runway, and disembarking the plane.

Another problem on the plane itself is that the ventilation and filtration systems are highly effective for removing Covid-19 aerosols from the air, but less so for the larger and heavier droplets that can also transmit the virus. That means if you’re sitting near an unmasked Covid-positive stranger who coughs or sneezes, their droplets could reach you before ever getting picked up by the ventilation and filtration system. “While [ventilation] is a really great layer of protection, the masks help pick up the slack,” Jetelina said.

“What we’re seeing in the science is that this proximity matters — a two-row diameter around you is where droplets could reach you from,” Jetelina said. “That’s quite a few people around you if you’re in the center of a plane.”

Finally, more masking on planes will help prevent community transmission when folks reach their destinations. Even if the number of individuals who are infected on the flight is low, each can then go on to infect a much bigger number of people. “Transmission on planes can really impact propagation within the community, and even across the nation,” Jetelina said. “And so, again, thinking about your individual level of protection is important, but also, the community-level protection that you have when you wear a mask on a plane.”

Jetelina said she doesn’t think people need to necessarily cancel flights now that masks are no longer required. “I think that if you wear a really nice N95 and if you’re boosted — or now it’s the second booster, so you’ve had four shots,” she explained, “there’s never no risk, but the risk is smaller with the layers of protection.”

Remember that you don’t need a mask mandate to wear a mask

When I recently interviewed biostatistician Lucy D’Agostino McGowan for an article about Covid-19 safety, she offered a helpful analogy she credited to her colleague Justin Lessler: When it comes to car safety, there are certain measures the government implements, like requiring that we all drive on the right side of the road and setting speed limits.

“They’re a minimum necessary requirement in order to keep our society functioning and allow people to get around in automobiles,” D’Agostino McGowan said. “And then there’s things you can layer on top of it, that will help your individual risk — both in terms of keeping you safe and keeping the people around you safe.” That might look like buying a car with a high safety rating, making sure your tires and brakes are in good shape, and cutting down on distractions like having a pet in your lap. It would be helpful for everyone if people thought of Covid-19 measures in a similar way and treated masks like something worth doing even if no one is forcing you to.

“What I’m afraid of is that when mandates are lost, the normalization is also lost,” Jetelina said. “And so I hope that people feel confident in wearing masks, even if there isn’t a mandate there. Because it is truly best for their health with these rising cases.”