You'll want to get your flu shot ASAP.

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 at least 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. 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.

When Exactly is Flu Season? Doctors Explain How to Prepare , portrait of a young woman in the winter forest. a beautiful girl sneezes into a napkin. get sick in winter.
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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 this year's flu season in order to best protect yourself.

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.

What will the 2021–2022 flu season look like—and how will it be different than the previous flu season?

Last year's flu season—technically the 2020–2021 flu season—affected very few people. By some estimates, the US only saw about 2,000 cases of the flu. By comparison, the 2019–2020 flu season saw an estimated 35 million cases and 20,000 flu-related deaths.

The culprit, as you probably guessed: COVID-19. With more people inside and masking up, flu transmission was greatly reduced—but that could spell trouble for this year's flu season for two reasons. First, as restrictions continue to lift, more people will venture out into public without the protection they had last year, Cassandra Pierre, MD, MPH, an infectious disease physician at Boston Medical Center, tells Health.

On top of that, those people—who spent most of last year in lockdown or greatly reducing their contact with others—may not have immune systems primed and ready for the flu. "Their immune systems may not be as primed to recognize and fight off influenza because we hadn't been exposed to it," says Dr. Pierre.

There's another issue, too, that's concerning infectious disease experts regarding the upcoming flu season: Australia didn't have a flu season this year. While their flu season down under is usually a good predictor of what flu season in the US will look like, an absent flu season can cause issues with vaccine production. "Usually when the powers that be are trying to figure out which strains to put in the vaccine, they are basing it on what circulated in the southern hemisphere during summer; they make a guess about what will come here," James H. Conway, MD, FAAP, a pediatric infectious disease specialist and associate director for health sciences at the Global Health Institute of UW-Madison, tells Health. This year, however, they're just guessing. "We don't have anything else to go on; we hope it's close enough," he says.

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

Each year, the flu shot for becomes available as early as late August, though mid-September is usually when you start seeing it advertised in drugstores and other places. "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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