Flu season might be starting to wind down—it generally goes from October to April—but vaccinations are still in full swing at drugstores (such as CVS, Rite Aid, and Walgreens), hospitals, and local clinics.

It takes up to two weeks for your body to build immunity after immunization. So is it too late to get a flu shot now, in early April, when flu season is practically over?

“Whenever I’m asked this question, I frankly get uncomfortable because there’s no recommendation not to do it,” says William Schaffner, M.D., a professor at the Vanderbilt University School of Medicine and consultant to the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices. “It is very late, but I would hate to think I’d discourage someone and then they got severe influenza a week and a half from now.” 

Graham Snyder, M.D., an infectious diseases physician at the Beth Israel Deaconess Medical Center and an assistant professor of medicine at the Harvard Medical School, echoes that sentiment. “It’s definitely not a waste to get a flu shot,” Snyder says, “in part because the immunity may be important in subsequent years, and it may even be important this year.”

Though flu activity is ramping down, Snyder says that people are still getting sick. He saw several patients in their 90s admitted to the ICU recently, one of whom didn't get the vaccine. “What if a month ago he had been thinking, ‘It’s March, the flu season is over and I didn’t get the vaccine’?”

This year’s flu season is turning out to be moderately severe because of the domination of the H3N2 strain, which tends to make people sicker, especially the elderly. But it’s following a typical trajectory in terms of duration, Schaffner says.

Flu season usually peaks from December through February or early March, and then winds down. But the timing of those peaks varies from season to season, Snyder says. Though the flu is on the decline overall right now, some areas are still experiencing little bursts of activity.  

When to Get Your Shot

The CDC recommends that most people get vaccinated as soon as the shot becomes available, which can be as early as late July. Ideally, you should get it by the end of October. But if you miss your shot in the summer or fall, the CDC says, you should still get it later in the season, even in January or after.

Of course, the vaccine isn’t always 100 percent effective no matter when you get it. Public-health experts predict which three or four flu viruses will be circulating months before a vaccine is developed. So you’ll be protected only against those viruses. If there’s a surprise virus, you might get sick even if you got the vaccine. And as with any virus, it's possible to get the flu twice in one season if you’re infected by two different strains, though that’s rare, Schaffner explains. Also rare, he says, is getting the flu as late as May or June.

If you get the shot now, it doesn’t mean you should skip next year’s vaccination, because that formulation may be different from this year’s. If you already got this year’s vaccination—even last summer—Schaffner says, you’re still protected and there’s no need for a second shot or a “booster.” The CDC says this year’s vaccine has reduced the risk of catching the flu by nearly half.