Yep, that means getting you flu shot—ASAP.

By Emily Shiffer
Updated December 23, 2019

Flu season is decidedly not  the most wonderful time of the year—the risk of incessant coughing and soldiering through an overall blah feeling for days or even weeks is enough to make anyone want to hibernate until...July.

But—sorry to be the bearer of bad news—you just can't do that. The only way to get through flu season unscathed is to get your flu shot. (You don't want to be one of the hundreds of thousands of Americans who are hospitalized each year from the flu, right? Right). While the efficacy of the flu vaccine varies from year to year, a 2018 CDC study found that the flu vaccine reduced the risk of adults being admitted to the ICU by 82%—that's a pretty big deal.

Here's the thing, though: In order to know when to get your flu shot (and, you know, be protected from the flu), you need to know when flu season actually is, how long it lasts, and when that all-important flu shot is even available. Here, infectious disease specialists weigh in on what you need to know about the flu in order to best protect yourself.

Okay, so when is flu season?

Technically speaking, you can get the flu year-round—it's when flu cases start to pick up that it's technically considered flu season. The CDC typically sets these standards by monitoring key flu activities (like outpatient visits, lab tests, and reports of hospitalizations and deaths). When those numbers remain elevated for a few consecutive weeks, it's considered flu season.

"Most of the time, influenza infections begin to increase in October and November and can last until May,” Alan Taege, MD, an infectious disease specialist at Cleveland Clinic tells Health. Later on, flu activity tends to peak even more—usually between December and January, and lasting until March—but "it's impossible to predict exactly when flu activity will pick up and taper off," says Dr. Taege.

Why does flu spike during colder months?

Of course, this is all relative (the winter months in California are drastically different than the winter months in New York), but, generally speaking, flu just likes the conditions of winter a little more. "The flu is a contagious respiratory illness, and the influenza virus lives longer in colder, drier air,” says Dr. Taege.

People are also much more likely to congregate indoors during the winter months (hello, more school and fewer vacations)—and that closer contact can help the virus spread, says Dr. Taege. But close quarters during other parts of the year can heighten flu risk too, like when lots of people gather on cruise ships for vacations, Richard R. Clark, MD, FAAFP, family medicine physician at Northwestern Medicine Grayslake Outpatient Facility tells Health.

When should I get the flu shot—and how long will it last?

Each year, the flu shot for becomes available as early as late August, though mid-September is more common. "The intent is to begin to distribute the vaccine before the onset of flu season, and we start as soon as we have the vaccine in order to vaccinate as many [people] as possible," says Dr. Clark.

The CDC itself has some pretty cut-and-dry recommendations for when to get your flu shot: ideally, everyone six months or older and able to, should get the shot by the end of October to have the most protection for when flu season begins. It's earlier than right when flu season starts (which, again, is typically in November), because it takes a while for the flu shot to actually kick in. "After vaccination, it can take two to four weeks for the antibodies that protect against the influenza virus infection to develop in the body," says Dr. Taege.

Still, if you just didn't get the chance to get the flu shot right away and suddenly find yourself unprotected from the flu in January, it's not an excuse to skip a flu shot that year altogether. Per the CDC, it's still beneficial to get vaccinated later in the year, into January and beyond, since you can technically catch the virus year-round.

The bad news? The flu shot won't last you an entire year. As a general rule “the flu shot is most effective in the first three months, [but] people still have protection after six months,” Vanessa Raabe, MD, pediatric infectious disease specialist at NYU Langone Health, previously told Health.

Your flu shot one year also won't protect you against the next year's flu (unfortunately). That's because each year, flu shots are developed in response to the prevalent strains for that year (typically a mixture of three different strains, along with some of the previous year's strains and new anticipated strains), per the CDC. Basically, each year the flu shot cocktail of sorts is different, and so it doesn't give the same level of protection.

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