Flu shots less effective in people who are obese, study finds

Here’s another health risk associated with carrying extra pounds: People who are obese get less protection from the annual flu shot, according to a study released Tuesday. But the authors said that people who are overweight or obese should get a seasonal flu shot anyway.

The study involved 461 patients who were vaccinated in 2009 at a clinic in Chapel Hill, N.C. By several measures, the vaccine appeared to wear off faster in people who were overweight or obese than it did in people of healthy weight.

For instance, 11 months after getting a flu shot, the level of flu antibodies in the blood had dropped by a factor of four in 25% of the healthy-weight subjects. But among obese subjects, 50% saw the same drop.

In another test, researchers tested the flu-fighting ability of subjects’ immune systems 11 months after getting a flu shot. They took samples of the subjects’ blood and exposed them to a flu virus, which should prompt the immune system to produce a protein called interferon-gamma. And it did, in 75% of the healthy-weight subjects. But only 25% of obese patients’ blood samples made the protein.

Study leader Melinda A. Beck, a professor at the University of North Carolina at Chapel Hill who studies how nutrition affects people’s susceptibility to infectious diseases like the flu, said everyone should still get flu shots because some protection is better than none.

“We absolutely recommend flu shots for everyone, including overweight and obese,’’ Beck said in an email.

She said researchers don’t have enough data to know why the vaccine appears to wear off faster in people who are obese. Perhaps the increased amounts of leptin (a hormone secreted by fat cells that helps regulate appetite) interfere with the function of immune cells, she said.

The study, published in the International Journal of Obesity, isn’t the first sign that flu is more dangerous in people with a high body mass index. During the H1N1 flu pandemic in 2009, obese people were more likely to contract the flu strain and die from the illness.

Beck said the new study could lead to development of a flu vaccine specially designed for obese people. One possibility, she said, is that obese people may require a higher dose of the vaccine, similar to the higher doses now offered to elderly patients.

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