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Can You Be Too Fat For the Flu Shot?

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We're coming up on flu season again, the annual holiday where we decorate our homes with piles of tissues and sing carols choked with phlegm. It's really not a very fun time—and one most of us would rather skip. But other than vitamin C and a prayer, our one defense is the flu shot.

Unfortunately, it can be hard to gauge exactly how much the flu vaccine will help, as its effectiveness varies from year to year. And now a new study, published in mBio, finds that its effectiveness may also vary from person to person. One factor that might make it less effective? Your weight.

Researchers from St. Jude Children's Research Hospital found that the flu vaccine didn't work in overweight mice. While the lean mice were protected from the virus by the shot, their overweight cousins fell seriously ill. When tested, it was found that the obese mice had lower antibody levels and higher levels of the virus. So in addition to being more likely to get sick, the overweight mice also had a harder time recovering as the virus penetrated more deeply into their lungs.

This raises serious concern about a similar effect in humans, especially as obese people already have a higher risk for complications from the flu, study author Stacey Schultz-Cherry, Ph.D., a member of the St. Jude Department of Infectious Diseases, said in a press release. "There is a critical public health need to translate these findings to humans and understand vaccine response in this growing segment of the population," she said.

The effect could possibly be remedied by either increasing the vaccine dose, making the dose dependent on the person's weight, or by adding adjuvants to vaccines to help magnify the body's immune response, but more research needs to be done in these areas, the paper concluded.

So does this mean that the flu shot is pointless if you're overweight? Mice aren't the same as humans, so we can't draw any direct connections yet. But it might be worth talking to your doctor to see if you're eligible for the higher dosage.