Why Do You Have to Get the Flu Shot Every Year?

Can’t you just coast on last year’s vaccine a little longer? (Sadly, no.)

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Every fall, you might start to notice signs in your pharmacy about getting the flu vaccine. You might be thinking, Already? Maybe I can skip it this year since I got it last year. This wishful thinking is tempting, but as of now, it’s still recommended to get the flu shot every year in order to have the best protection against the seasonal flu.

Different vaccines are effective for different amounts of time. There are some vaccines you only need once as a baby, while others need “boosters” as the years pass. The flu vaccine is not a one-and-done shot—at least not yet.

Why Do You Need a Flu Shot Every Year?

You may know the illness as “the flu,” but this infection is actually caused by one of many strains of the influenza virus. These viruses mutate regularly, making them hard to “pin down” and target with a single vaccine.

Plus, different strains are more prominent each year. Throughout every year, experts track which flu viruses are circulating in animals, especially birds, bats, and pigs. Flu viruses can easily jump from these animals to humans (hence “bird flu” and “swine flu”). If a certain strain is widely circulating in bats one summer, there’s a good chance it will soon be circulating in humans.

Scientists then use this information to design the annual flu vaccine. Every year, they target the flu shot toward the flu strain that they predict will circulate in humans. In other words, the flu shot you got last year protects against the dominant flu strains last season—so it might be useless against this season’s flu virus.

Finally, the flu shot only provides protection for a limited time. You may not still have influenza-fighting antibodies in your system a year later, even if the exact same flu strains were circulating. This would make you vulnerable to catching the flu and potentially having life-threatening complications.

The Potential for a New Kind of Vaccine

Researchers have long been interested in a “universal” flu vaccine. The idea is to have one shot that could provide protection against all or most flu strains for several years at a time. This could improve vaccination rates, which means the flu would be less of a burden to society.

Until then, get the flu shot every year. It’s best to get the vaccine in the fall before flu season really gets going. That way, you’ll have the best chance of enjoying a flu-free year, and you’ll reduce your risk of spreading the flu to others.