Last year, public health experts were deeply concerned about the prospect of a flu and a COVID-19 “twindemic.” But as it turned out, seasonal flu activity was unusually low. This was likely due to the combination of masking, stay-at-home orders, reduced travel and people paying close attention to things like indoor ventilation.

No one yet knows what the upcoming flu season will hold, especially with states’ differing approaches to masking and social distancing.

But one thing is clear: Health guidelines continue to state that anyone ages 6 months and older should get their annual flu vaccine. And that means millions of people will get their flu shot at or around the same time they get a COVID booster dose (or, for some, their very first shot of the coronavirus vaccine).

Is that safe? Is there anything people should know about getting two vaccines at or around the same time? Here’s what we know.

If you’re eligible for a COVID vaccine, you can absolutely get one at the same time that you get the flu vaccine, according to the Centers for Disease Control and Prevention.

That’s true whether you’re getting your first or second shot of either of the mRNA vaccines (Moderna and Pfizer), or the one-shot Johnson & Johnson vaccine. And it’s very likely to hold true if and when booster shots roll out as well — although the Food and Drug Administration has not yet approved them, and booster shots are not without controversy.

“There’s no reason you cannot get both at once. They are not going to counteract each other in any way,” Karl Minges, dean of the School of Health Sciences at the University of New Haven, told HuffPost. “COVID vaccines are using a very different mechanism to vaccinate an individual than the influenza shot.”

In fact, Moderna recently announced it is working to develop a joint flu shot and COVID-19 booster, combining its existing COVID vaccine with an experimental flu vaccine.

“The two-for-one approach is really appealing, especially if that becomes available to people who are scared of needles or don’t have the time to go to a doctor’s office or clinic or pharmacy to get two shots,” Minges said.

The most common side effects of the flu vaccine include soreness or redness at the injection site, headaches, fever, nausea, muscle aches and fatigue. Those symptoms overlap a lot with the most common side effects of the COVID vaccine and booster dose.

If you get both shots at the same time (whether an initial dose of the coronavirus vaccine or a booster), they will likely be given in different arms, so you don’t have one spot that’s really red and tender.

“Everybody’s response is a little bit different, but those after-effects from any vaccine are possible, and it would seem logical that if you had both of them co-administered that you might experience a little bit more of those after-effects, although that varies a lot from person-to-person,” said Aaron Clark, a family medicine physician at the Ohio State Wexner Medical Center and medical director of the Ohio State Health Accountable Care Organization.

People who get both vaccines at once might experience a bit more achiness or feel more feverish, Clark said. But most side effects of both vaccines are mild and pass within a day or two.

Clark added that the 2021-22 season’s flu vaccine has just started rolling out, so there isn’t yet a lot of national data on people who get both shots at once are experiencing. He emphasized that the bottom line is that both the flu vaccine and the COVID vaccines are safe and effective.

“Co-administering vaccines is a very common tactic that we do,” Clark said.

It’s not possible to plan your flu shot timing around when you might get a COVID booster yet. That’s because even though booster doses have been recommended by the Biden administration, they haven’t yet been authorized by the FDA. Still, they could start rolling out in a matter of weeks to people who are eight months out from their last dose.

In general, September and October are the ideal times to get a flu vaccine. Experts always emphasize that it’s absolutely still worth getting a shot later in the fall or winter, because flu season can peak in March and last until the spring.

“I would say it’s always better to get the flu shot earlier, no matter the season,” Minges said. He added that one byproduct of the minimal influenza activity around the world last year is that experts have less information than usual to decide which specific flu viruses to include in this year’s vaccine.

But that’s not a reason to avoid getting the flu shot. And besides, there’s no way to know how bad this year’s flu season will be.

“The best defense against influenza and COVID-19 is vaccination, number one,” Clark said. “And safe social distance, wearing masks, frequent hand washing, not going to school or work when you’re sick are all things we can continue to do to protect ourselves.”

Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.