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How Effective Is the Flu Vaccine?

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But the sooner you get it, the better. Why? Simple: the further you get into the flu season, the higher your risk of getting flu. Here’s something else to keep in mind: it can take two weeks for the flu vaccine to take effect. So if you’re exposed to the flu within that two week period, you might still get sick.

Once a flu season is over, the old vaccine is not as effective, so an annual flu shot is needed for optimal protection.

How Well the Vaccine Is Matched With the Dominant Flu Strains

Unlike other vaccines, the flu vaccine is often updated each season to protect against what researchers believe will be the dominant strains of the flu that year. Predictions are based on world-wide monitoring of viruses. While predictions are generally accurate, they aren't foolproof. The effectiveness of the flu vaccine in a given year depends on their accuracy. 

Unfortunately, getting the flu vaccine isn’t a guarantee that you won’t get the flu, but it is thought to provide at least partial immunity. If you catch the flu despite getting the vaccine, your symptoms may be milder. 

So, don't skip the vaccine -- especially if you're at high risk for flu complications. Even though the flu vaccine may not work quite as well in young children, older adults, and the ill, these very same people are the most likely to have severe and even life-threatening complications from the flu. It’s crucial that they get vaccinated. While it may not be perfect, the flu vaccine is the best defense we have.

One more thing to keep in mind: the flu vaccine does not protect against cold viruses. Some people believe that the flu shot doesn’t work because they get sick despite being vaccinated. But in most of these cases, experts say, the flu vaccine did work -- it’s just that these people came down with an unrelated cold virus.

WebMD Medical Reference

Reviewed by David T. Derrer, MD on September 01, 2014
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