Being obese may impair the body’s ability to mount a protective immune response to the flu, according to a newly published study in the International Journal of Obesity.

The study, conducted at the University of North Carolina, Chapel Hill’s Department of Nutrition at the Gillings School of Global Public Health, found that the initial immune response from the flu vaccine is intact in both healthy and obese people 30 days after inoculation.

But at some point after that it begins to decline dramatically in the obese population.

In the study participants, 12 months after inoculation the antibody had declined more than fourfold, said Patricia Sheridan, a nutritional immunologist and professor and the lead author of the study. Specifically, 50 per cent of the obese participatns saw a fourfold drop in antibody levels at 11 months; only 25 per cent of healthy-weight participants saw a similar drop.

“Naturally the antibody declines over time for everyone,” Sheridan said in an interview with the Star. But it seems to be more pronounced in the obese and overweight.

This could be of concern if the decline occurs while flu season is underway. “If you get vaccinated in September and the virus doesn’t circulate until March, you may also be more susceptible,” she explained.

The study also found that the CD8-T cells (which fight the flu virus) in obese individuals don’t work as well as in individuals who are not obese.

To better understand the effect of weight on the antibodies, Sheridan and others are mounting a study of 4,000 people.

She hypothesizes the reason for the lack of vigour in the CD8-T cells may be tied to either leptin, a hormone produced by fat, or pro-inflammatory cytokines.

Sheridan and her team aren’t suggesting that obese people shouldn’t get the flu shot. Far from it. “What we really think is as it stands the flu vaccine for everyone over 6 months old is the best prevention for getting the flu,” she said. “We don’t think overweight and obese people should be concerned that getting the flu shot won’t work for them. But it does suggest that if you’re overweight or obese it’s important to lose weight.”