“The problem, as it stands right now, is this Omicron is a new variant that’s spreading very fast,” Dr. Frank Esper, an infectious disease specialist with the Cleveland Clinic, told Fortune. “This is unfortunately just a terrible time to have a bad wave of a new variant here in the United States.”

When it comes to readjusting holiday plans, medical experts say the decision will likely come down to individual risk tolerance. At this point, the evidence shows that Omicron is more transmissible than previous variants. But so far, infections seem to be less severe for vaccinated people, with fewer hospitalizations and deaths being recorded. 

But that doesn’t mean that Omicron will simply be like a mild flu for everyone infected, says Dr. Abinash Virk, one of the Mayo Clinic’s top infectious disease experts and former head of its travel clinic. 

“Everyone keeps saying, ‘Oh, it’s a mild infection,’” notes Virk. “Well, yes, it’s a milder infection for most people, but it’s probably not going to be a mild infection for people who are vulnerable, and there are vulnerable people around us.” That includes those who are unvaccinated, elderly Americans, as well as those with pre-existing conditions that could lead to more severe cases. 

For those who are already vaccinated, the COVID vaccines have been shown to be about 30% effective in preventing infections of Omicron and 70% effective at protecting against severe hospitalization. That protection increases among those who received a booster, but particularly for people who received a Moderna booster, a new study shows.

“The protections that we had from the vaccine have already been shown that it’s not as good against this Omicron variant. Boosters have shown to be helpful, but we don’t necessarily know for exactly how long,” Esper tells Fortune. 

What does that mean for those with holiday plans? “If you don’t have to travel, don’t travel. That’s the easiest one,” Virk tells Fortune. Younger, healthier Americans who have been vaccinated and boosted and wear a mask may be better off, but there’s always a risk. 

If you’re still unvaccinated, or at higher risk for a severe case of COVID-19, then you should reconsider travel on public transportation right now. “Those who are vulnerable or have a higher risk could maybe consider canceling the trip if it’s totally optional. It’s just that the risk of picking up something is a lot higher if it’s Omicron,” Virk says.

No matter what, it’s best to take extra precautions since Omicron is both more transmissible and is causing illness even in those with immunity, says Dr. Jessica Justman, associate professor of medicine in epidemiology at Columbia Mailman School of Public Health.

If you are planning to travel this week or attend holiday celebrations, here are a few words of advice from leading medical experts. 

Mask up!

When it comes to getting COVID-19, no matter what the variant, your chances of being infected are higher if you breathe in more particles. It’s a numbers game. That’s why masks are effective—they reduce the number of particles you breathe in. And masks protect both the wearer and the people around them, according to the University of Michigan’s medical school. 

“We really need to start getting good about wearing those masks—even when we’re just running in and out of the gas station or the grocery store or convenience store. A lot of times we say, ‘It’s just gonna be in and out. I don’t need to wear a mask.’ Now is the time where we really need to think about doing that,” Esper says. 

It’s worth noting that although only a few states have a mask mandate at this point, the Transportation Security Administration still requires travelers to wear masks on airplanes, trains, buses, as well as in airports and train stations, through March 18.

Top U.S. infectious disease expert Dr. Anthony Fauci said Sunday during an interview on ABC News’s This Week that “even though you have a good filtration system, I still believe that masks are a prudent thing to do, and we should be doing it.”

Experts say that everyone, whether vaccinated or not, should be wearing a mask, and wearing it properly. “It’s extremely important to wear a mask that fits snugly and is comfortable enough that you will really wear it,” Justman says.

And if you’re traveling or going to be in a crowded indoor space, Virk says it’s worth using an N95 mask. “I would recommend considering an N95 for travel because that’s really the maximal protection that’s going to be available beyond the vaccinations,” she says. 

Getting tested is worth it

If you’re planning on traveling or attending holiday festivities, it’s worth getting a COVID test ahead of time. “Getting tested before you go is going to be very helpful,” Esper says. 

And that’s true whether you’re having symptoms or not. There are still plenty of asymptomatic COVID cases. “There’s really no way of differentiating, you know, COVID from influenza at this point, and it would be important to get tested,” Virk says. 

Roughly one in four Americans is already planning on asking family and friends to get a COVID test before holiday visits. About 63% of Americans say that if asked, they would take a COVID test before visiting family, according to a recent poll by Rapid Test & Trace USA published last week. 

When it comes to the type of test you should get, Esper says PCR tests are more accurate. “The home tests only really shine when you’re actually having symptoms,” he says.

But it may be difficult to schedule a PCR test at this point. If that’s the case, an at-home test—typically an antigen test—is better than nothing. “More information is better than less. The test kits are not perfect, especially if you are asymptomatic, but they are much better than the alternative, i.e., not knowing that someone has an infection,” Justman says.

Along with testing, consider who you’re hanging out with at holiday functions as well. “With Omicron in the mix, this is not the time to include your unvaccinated friends and relatives at indoor family gatherings, even if you feel like you might be rude by uninviting them. This is to protect them and to protect you and your family,” Justman says.

Those visiting elderly relatives and unvaccinated children should also double-check to make sure holiday plans are still a go, especially since these individuals may be at higher risk for a severe infection.

Get a booster, even now 

Both Esper and Virk say that even though the vaccines are not as effective against Omicron infections compared with previous variants, it’s still worthwhile getting vaccinated and boosted to prevent a severe case.

At this point, medical experts are recommending that anyone who can get a booster—currently those age 16 and older—should get one. “Anybody over the age of 16 should get a booster,” Esper says. 

But keep in mind that boosters take about two weeks to be fully effective. “It’s not like turning on and off a light switch. If you get your booster now, it still is going to take somewhere between seven to 14 days before you actually get the protection that you want,” Esper says. 

That doesn’t mean it’s worthless to get one. “If you’re planning on holiday travel late this week, early next, getting a booster dose can certainly help during those travels,” Esper adds. 

You will improve your immunity with a booster, according to Virk. “It would still give you some protection,” she says. “You’re boosting. It’s not like you’re starting from scratch. You will improve that immunity and hopefully if you do end up getting infected, it will be a milder episode as opposed to not having a booster at all.”

At the end of the day, Justman says, Americans should consider holiday travel very carefully. Ask yourself: How important is it to travel now? Can you possibly reschedule for a visit later, when we have the next pause in the variants? “I canceled my plans over the weekend to visit family in the U.K. because of the COVID-19 risk there. [And] will reschedule at a later time,” she says.