Excess Weight Impairs Immune Response, Reduces Flu Shot Effectiveness

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One of the most prevailing myths that keep Americans from getting an annual flu shot is the thought that the vaccine causes the flu. The CDC reiterates each year that the vaccine does not contain live virus so it cannot cause symptoms, but researchers in North Carolina have recently found that a condition that affects two-thirds of Americans can reduce the effectiveness of the flu shot – excess body weight.

Melinda Beck PhD, a professor and associate chair of nutrition at the University of North Carolina at Chapel Hill’s Gillings School of Global Public Health, and colleagues studied people who were vaccinated in their clinic in 2009 with inactivated trivalent influenza vaccine, the common flu shot for that fall and winter season. The patients were followed nearly one year after vaccination and gave blood samples to test for antibody levels.

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All patients receiving the vaccine developed antibodies to flu viruses within the first month after vaccination, however, the antibody levels in those who were overweight and obese declined more rapidly over time. About 50% of obese participants had a four-fold decrease in antibody levels at 11 months compared to one month post-vaccination compared to less than 25% of healthy weight volunteers.

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In addition, the response of CD8+ T-cells, a type of white blood cell that plays a key role in the immune system, appear to be defective in heavier people. When vaccination fails to prevent flu infection, the body relies in part on these cells to limit the spread and severity of illness.

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"These results suggest that overweight and obese people would be more likely than healthy weight people to experience flu illness following exposure to the flu virus," said Dr. Beck. "The findings also suggest overweight and obese people are more likely to become sicker and have more complications,” adds Heather Paich, a doctoral student involved in the study.

Influenza is a serious public health threat, causing three to five million cases of severe illness each year and killing up to half a million people annually worldwide. In addition to receiving the flu shot each year, the CDC recommends the following “everyday preventive actions” to stop the spread of germs that cause illness:

• Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
• Wash your hands often with soap and water. If soap and water are not available, use an alcohol-based hand rub.
• Avoid touching your eyes, nose and mouth. Germs spread this way.
• Try to avoid close contact with sick people.
• If you are sick with flu–like illness, CDC recommends that you stay home for at least 24 hours after your fever is gone except to get medical care or for other necessities. (Your fever should be gone without the use of a fever-reducing medicine.)
• While sick, limit contact with others as much as possible to keep from infecting them.

Source References:
P A Sheridan, H A Paich, M A Beck et al. “Obesity is associated with impaired immune response to influenza vaccination in humans”, International Journal of Obesity advance online publication 25 October 2011; doi: 10.1038/ijo.2011.208
Centers for Disease Control and Prevention: Take 3 Actions to Fight the Flu

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