As the weather gets chillier and people spend more time indoors, COVID is once again not-so-gently rapping at the door.

COVID cases in the U.S. are fairly flat at about 38,000 cases a day right now, but a slew of new Omicron subvariants could drive another fall or winter surge, experts say. And the best way to protect yourself is to get a new bivalent booster shot. The new boosters target both the original strain of SARS-CoV-2, the virus that causes COVID, as well as the Omicron BA.4 and BA.5 subvariants. Scientists expect them to provide broad protection against newer variants as well.

Immunity from prior infection or vaccination wanes over time. And people who are elderly and those with underlying health conditions are especially vulnerable to severe disease. Yet fewer than 10 percent of people in the U.S. who are eligible for the new boosters have gotten them.

Scientific American spoke with Hilary Marston, chief medical officer for the U.S. Food and Drug Administration, about why booster uptake has been so abysmal, what we know about how effective the shots are and why it’s still so important to get one.

[An edited transcript of the interview follows.]

Why are these boosters so crucial, and who is eligible for one right now?

Obviously, the importance of booster shots just couldn’t be greater than at this moment, as the weather is getting colder and we’re all inside more. And we have—thankfully—access to these safe and effective vaccines that are honed to target updated strains. I think we’re very fortunate in this country to have that, and I do really, really encourage people to avail themselves of it. Currently, the updated Pfizer vaccine is available to everyone age five years and up. And the Moderna vaccine is available to those ages six years and up. There are a couple of caveats on that. Number one is, if you’ve recently gotten a booster with the original strain—the ancestral strain, as we call it—we recommend that you wait two months after that before getting the new booster shot. And for individuals who have recently had an infection, it’s a recommended three-month wait.

Why do you recommend the wait?

The reason we do that is to ensure that you get the best immune response you can get out of these vaccines. If they’re spaced too close together, the concern is that you might not get as much of an immune effect from it, but also that any safety concern that there could possibly be could be magnified by putting them closer together. I do want to emphasize that these vaccines are incredibly safe; we’re talking about tweaking at the edges there. But the best way to get it that optimizes all of those factors is to wait those two or three months.

As of a week ago, only about 5 percent of Americans who are eligible had gotten their booster shot. Can you comment on that?

Would I like to see the numbers higher? Absolutely. And I think any health care worker would and anybody who’s been following this pandemic very closely. As a health care worker, boy, I feel for those who are in the emergency rooms on the front lines. They’re going to be there to take care of you if you do get sick, of course, but it is just such a strain. And it is frustrating, because we have tools, we have more than we could have possibly hoped for at the beginning of this pandemic. And it’s frustrating to see the boosters not getting into arms.

Children under five have been eligible for the vaccine since mid-June, but fewer than 5 percent have been fully vaccinated. Why do you think the uptake has been so low? And what would you say to parents who haven’t vaccinated their child?

I think the reason is multifactorial: everyone’s making decisions for their own children. But I think it’s at least in part based on the misperception that COVID is overall not something to be concerned about in kids. And that’s something that I really want to take head-on. There’s no question here that the people who are getting very sick from COVID-19—and we’re still seeing more than 300 deaths on a rolling basis in this country every day—those folks are largely the elderly unvaccinated with comorbidities. But that’s not to say that there’s no risk in children.

There is, for example, a higher risk of hospitalization and deaths than we see from influenza, and plenty of us are rushing out to get our kids vaccinated against the flu. So I would encourage parents to look at it as something that they should do, just as they would protect their children from flu. We were fortunate in this country to have access to these vaccines.

There’s the infection itself, but then there’s the potential for long-term consequences from getting infected. For example, the risk of long COVID is something that we’re trying to understand better, even if it’s pretty rare. If we’re talking about large populations getting infected, then there will be a number of children affected by long COVID. These are the sorts of things I’d encourage parents to look at as they’re considering the choice to get their children vaccinated.

The risk of severe COVID increases with age. Do you think that people over 65, people with comorbidities or people who are immunocompromised should race to get a booster shot?

Absolutely. This is the single best thing that you can do to protect yourself against this virus. We have these vaccines widely available. People should be going out and taking advantage of this program. The risk is certainly higher in those populations. And we continue to see as we look at those folks who are hospitalized, who are dying from COVID, it is overwhelmingly people who have either not been vaccinated at all or have not been boosted. So I would certainly strongly suggest that people go to and find a local spot to get your vaccine.

Do we have any data yet on the real-world effectiveness of the updated bivalent booster?

What we have from the FDA authorization was based on immunogenicity data—the ability to generate an immune response. We are on the lookout for data as they become available in the setting of the currently circulating strains. So we will be putting that out. This is kind of the perfect moment for folks to go out and get those vaccines. We’re about a month out from Thanksgiving right now. So what better time to get your updated vaccine so it will have that maximum effect as you’re getting together with your loved ones around the table?

We already have several new variants circulating. Do we know anything yet about how well the vaccine works against them?

The data are emerging. What happened with every past variant is the data evolved over the course of time. But it’s something we’re looking at closely. I think we’re confident that having the updated vaccines places us in a much better position than we would have been in just using ancestral virus strains. But the specific amount of immune evasion is something we’ll continue to watch. The most important thing here, though, is how well the vaccines are protecting against severe disease. They can only do that if people get those shots in their arms.

Is there any message that’s not getting out there that people should hear?

I think that the best way for everyone to protect themselves is to go out and get their COVID vaccine and get their flu shot. One of the best clinical teachers I had in my training would tell people to go get their flu shot around the time when the Halloween candy came out. We’re definitely in that time. Protecting yourself against the flu is certainly something we should do every year. But there is potential, based on what happened in the southern hemisphere, that this could be a bad season. So please, please, please do that. And at the same time get your COVID vaccine. We’ve made it really easy for folks in the U.S. All the local pharmacies are carrying both vaccines. So don’t hesitate to do it.

The vaccination program broadly has been focused on health equity, and trying to ensure that all populations have great access to these vaccines and are using them. And something else we’re going to continue to emphasize is, for vulnerable populations, ensure that you have a treatment plan in case you do get infected—particularly for folks who are immunocompromised. Go out and talk to your doctor, and make sure that if that home test does pop up positive, you know exactly how you’re going to go and get treatment.

Early in the pandemic, Black and Latino populations had less access to COVID vaccines and were vaccinated at lower rates. But now that ratio has flipped—the white population, which is more skeptical of vaccines, is less vaccinated, proportionally. Can you comment on that?

I think that access was the first issue we needed to solve. And scarcity is the worst barrier to access that you can have. But thankfully, we’re not in that position anymore. The next barrier is combating misinformation. And that’s part of what we’re trying to do here today—making sure that people have the best information to make decisions themselves to protect their loved ones.