(CNN) Despite warnings from public health officials, millions of Americans traveled over the Christmas holiday. The US Transportation Security Administration reported that nearly 1.3 million people passed through airport security checkpoints nationwide Sunday.
This record-breaking development in pandemic air travel comes as the United States has surpassed 19 million coronavirus infections. And December marks the deadliest month since the start of the coronavirus pandemic.
CNN Medical Analyst Dr. Leana Wen, an emergency physician and visiting professor at George Washington University Milken Institute School of Public Health, explains how people can still take precautions to keep themselves safe and to reduce the spread of Covid-19 in their home communities.
CNN: Christmas may be over, but New Year's is this week. What's your advice for reducing risk during the rest of the holidays?
Dr. Leana Wen: People should keep in mind the concept of cumulative risk, that risk is additive: The more high-risk activities you participate in, the greater your likelihood of contracting Covid-19 (and, if you are an asymptomatic carrier, to inadvertently infect other people). Just because you've engaged in one high-risk event doesn't mean you should engage in others. So let's say that you had Christmas dinner with extended family and friends. That doesn't mean you should also now go to a bar or crowded New Year's Eve party.
For the remainder of the holiday, if you've traveled, you should try to reduce risk in other ways. See people outdoors only, households separated at least 6 feet apart. If you have to be indoors, make sure you have masks on the entire time. Stay away from settings where others have their masks off and are not abiding by physical distancing guidelines. Take every precaution when traveling.
You may have had risk from the one or two activities you already engaged in, but you can still prevent further risk the rest of the holiday.
CNN: What about when people return home after traveling — do you recommend a quarantine?
Wen: Yes. You could have had risk through getting together with others at celebrations and through the travel itself. The last thing we would want is for travelers to then seed coronavirus once they return home, to their family, colleagues, friends and neighbors.
I recommend to quarantine for seven days and to get a coronavirus test at that point. The CDC (Centers for Disease Control and Prevention) says that you can get a coronavirus test three to five days after travel. That's probably enough time for the test to turn positive after exposure, though waiting for seven days will pick up even more infections. If you're unable to get a test because of limited testing in your community, you need to quarantine for a full 10 days.
CNN: This seems extreme. Is it really necessary?
Wen: Unfortunately, yes. There is such a high level of coronavirus in most parts of the country that being in a crowded airport and plane exposes travelers to risk. Loved ones are also just as likely as strangers to have coronavirus, so if you were indoors with friends or family who don't live in your household, you were also engaging in a high-risk activity.
Our hospitals are at the brink. One in five hospitals are reporting that their ICUs are full or nearly full. When hospitals are filled, it's not only patients with coronavirus who suffer; other patients who need care for heart problems or who come in after car accidents also get delays in their care.
Hospitals are the last line of defense. The community is the first line of defense. Quarantine and testing after a high-risk exposure is the best thing you can do to prevent further overburdening our health care system.
CNN: What would be considered high-risk activity?
Wen: Travel itself is high risk unless you drove with just your household in a car. Buses, planes and trains, especially for holiday travel where there are so many other travelers, would have risk of coronavirus exposure.
Many people, after traveling, probably gathered in some way with their relatives and friends. If the only gatherings were outdoors, following physical distancing, that's not high risk. However, if there were any indoor gatherings, those would be high risk. Consider activities that would be normal in pre-pandemic times. People sitting around the dinner table, masks off, eating for long periods of time. Or watching TV together sitting on a couch or having drinks while preparing a meal. These are all high-risk activities.
There are nuances here. If, for example, everyone that you saw has also been quarantining and did not see anyone else for at least 10 days before getting together, that would substantially reduce risk. But if everyone has just had one negative test alone, that in itself is not enough. A negative test must be accompanied by at least seven days of quarantine before that. If in doubt, you should consider your exposure to those you saw indoors to be high risk and quarantine accordingly.
CNN: What if you live with someone and they didn't travel with you?
Wen: When you return, you should quarantine from them to prevent transmitting coronavirus to them. (And, if they traveled themselves or were engaged in high-risk activities, too, they should also quarantine.) Quarantining from people you share a home with isn't easy, but it can be done.
Try to avoid going to shared spaces at the same time, like the living room. When in those spaces, wear a mask. Wipe down commonly used surfaces like door handles or faucets. Keep windows open as much as you can. Take extra precaution if you live with someone who is at high risk for illness, if they are older or have chronic medical conditions.
CNN: Can I still go grocery shopping or bring my kids to school during quarantine?
Wen: No. A quarantine should be strict: Do not go into public spaces where you could infect others. That means not going to grocery stores or to work. Kids should not go to school or day care. And definitely do not get together with anyone else who is not in your immediate household during this time.
CNN: Does it matter if I'm healthy, or the place where I'm returning to has a high level of coronavirus already?
Wen: Even those who are previously healthy could get ill themselves. They could certainly spread coronavirus to others unknowingly. Our health care system is already so strained that we really cannot afford further escalation in infections. This is particularly true in areas that are hotspots, but many other areas are on the cusp of having explosive spread, too.
That's why it's up to all of us to do our part. If we traveled or otherwise saw loved ones over the holidays, we should quarantine and get tested. That way, we protect ourselves and those around us, and we reduce the level of coronavirus spread in our home communities.