How Long Is the Flu Vaccine Effective?

The flu shot can last for up to six months, though it is most effective for the first three months.

If you find yourself with those typical flu-like symptoms—fever, chills, nasal congestion, the works—you might start worrying that you've come down with the flu (yep, even when it's not flu season).

Wait: Didn't you get the flu shot last year? And if that's the case, how long does a flu shot last, exactly—and are you still covered?

Here's how long the flu shot is effective and what that means for when you should get your next one.

What Is the Flu?

The flu, or influenza, is a contagious infection of your lungs, throat, and nose. It infects millions of people every year. More people get sick at certain times of the year, especially late fall through spring.

Symptoms come on fast and can include:

  • Cough
  • Runny or stuffy nose
  • Feeling tired
  • Body aches or headaches
  • Sore throat
  • Runny nose or congestion
  • Vomiting and diarrhea (more common in children)

People can spread it before they have symptoms and up to five or seven days after they get better (which can also take several days). You get it by touching a contaminated surface and then touching your nose or eye. People who are sick can also spread it when talking, coughing, or sneezing.

Who Should Get a Flu Shot?

Most national health organizations recommend that anyone 6 months or older get a flu shot yearly, except in rare cases.

The Centers for Disease Control and Prevention (CDC) especially recommends that you get the flu shot if you are older than 65, pregnant, have had a stroke, or have a chronic condition including (but not limited to):

  • Asthma
  • Diabetes
  • Chronic kidney disease
  • Heart disease

How Long Does the Flu Shot Last?

In short: The flu shot can last as long as six months. The long answer is a little bit more complicated, partly because everybody is different.

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, told Health.

Knowing how long the flu shot lasts is essential in determining when to get your flu shot each year. Flu season generally lasts from October to May but peaks from December through February.

The CDC recommends getting the flu shot by the end of October.

Unfortunately, if you get your flu shot in October of the previous year, you're not covered the following October (and yes, that can matter since the flu technically exists year-round and only peaks during the flu season).

If you got your shot later in the season of the previous year, such as March, unfortunately, you're still not really covered at the end of the year of that year, even if you're within the six-month range. The flu strains differ yearly (and so do the vaccines).

How Effective Are Flu Shots?

Researchers "tweak" vaccines annually to account for changes in circulating strains. Even so, vaccine effectiveness can vary widely from year to year.

For instance, the CDC estimated the flu shot's effectiveness at 56% during the 2009-2010 flu season, 60% during the 2010-2011 season, and 36% in 2021-2022. The U.S. Food and Drug Administration, which approves vaccines, doesn't expect or guarantee the vaccine will entirely prevent the flu. Several studies have also shown that vaccine effectiveness decreases each month after you get it.

Still, the vaccine makes severe illness and hospitalization less likely, especially if you have a condition that makes you more vulnerable.

It's best to get the flu shot yearly—unless you're severely allergic to the vaccine or are six months of age or younger. While the flu shot isn't 100% effective, it can prevent the flu from becoming fatal.

A Quick Review

The flu shot is effective for about three to six months. And because the flu makes millions of people sick each year and is pretty contagious, health organizations recommend that nearly everyone older than 6 months get a flu vaccine annually, preferably around the start of flu season.

While the shot won't fully protect you, it reduces your odds of getting it or getting very sick, especially if you are in a high-risk group. If you have any questions or concerns about getting a flu shot, reach out to your healthcare provider.

Was this page helpful?
Sources uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Seasonal influenza (flu) vaccination and preventable disease.

  2. Medline Plus. Flu.

  3. StatPearls. Influenza.

  4. Centers for Disease Control and Prevention. People at higher risk of flu complications.

  5. Centers for Disease Control and Prevention. Flu season.

  6. U.S. Food and Drug Administration. Seasonal flu (influenza) and the FDA.

  7. Centers for Disease Control and Prevention. Prevention and control of seasonal influenza with vaccines: recommendations of the advisory committee on influenza practicesUnited States , 2022-23 influenza season.

Related Articles