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Vaccines Health Center

Your Questions About the Flu Vaccine

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Why Do I Need to Get Vaccinated Every Year?

You might balk at having to visit your doctor or pharmacy every year for yet another dose of the influenza vaccine, but there's a good reason for the repeat visits. The flu bug is a pretty wily creature.

"The virus is sort of tricky in the way it reproduces from year to year, in that it shifts its chemical coating from season to season," explains Geoffrey A. Weinberg, MD, a pediatric infectious disease specialist and professor of pediatrics at the University of Rochester. "Even if you've been good about getting flu shots for several years you need to keep it up, because next year's flu could be very different."

The flu is far less predictable than measles and chickenpox, which only take a couple of childhood immunizations to provide full protection. "Those diseases are caused by only one strain of virus, and they don't shift," says Weinberg.

That annual flu vaccine ritual might soon be coming to an end, however. Researchers have been on the hunt for a universal flu vaccine for several years, and they may be getting close. Recently, they've discovered a more consistent target on the flu virus -- one that could help them finally develop a flu vaccine that provides long-lasting protection.

How Well Will the Flu Vaccine Protect Me Against the Flu?

Each spring, public health experts around the world predict which flu strains are most likely to circulate and cause illness in the coming flu season. Based on their predictions, the flu vaccine is formulated to protect against those three or four strains. When the experts have made a good match, the vaccine is up to 90% effective in healthy adults. For those age 65 and older, a high-dose version of the flu vaccine called Fluzone is recommended when available. It may be more effective at protecting the elderly because their immune systems are more fragile.  

Sometimes the flu virus will outsmart the experts and transform itself between their prediction and the beginning of the flu season. It might even change in the middle of a flu season. Then the flu strains in the vaccine won't match the strains in circulation.

Even if the vaccine isn't a perfect match it's still worth getting, experts say. Each vaccine protects against three to four different flu strains, so chances are at least one of them is circulating in any given season. Plus, when you get vaccinated against one strain of flu virus, your body makes antibodies that protect you against related strains, even if they're not exactly the same.

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