Why Do You Feel Bad After a Flu Shot?

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Dr. Michael Smith
If you’ve gotten your annual flu shot, nice work. More than 200,000 Americans are hospitalized because with the flu every year. But you still can catch the flu after a flu shot, and here are some reasons why. Every year scientists decide what flu strains will be most common during the flu season. The vaccines take at least 4 months to produce, so they have to make their best guess pretty early. Even in a well-matched year, the flu vaccine is only 60 to 90 percent effective. The CDC announced this year’s flu vaccine only covers 50 percent of the strains floating around. So if you come in contact with a virus very different from the vaccine, it may not protect you. It’s also possible to catch the flu before the flu vaccine takes effect, usually about 2 weeks. Some believe you can catch the flu from the flu shot, but that’s just a myth. It’s normal to have some side effects like soreness where the shot was given. It’s rare, but you may also get a low grade fever or feel some aches. They will probably only last 1 to 2 days, and then you’ll be back to normal. If you have different symptoms than aches after a shot, you may have caught a cold. Remember its cold AND flu season. Still, the benefits of getting a flu shot far outweigh the risks. Even in a down year like this one, you’ll be protected against half of the viruses out there. For WebMD, I’m Dr. Michael Smith.