Health

Flu shots fade in obese

Obesity may limit the effectiveness of flu vaccines, say researchers who tested blood samples from people of various weights over a year.

Obesity may limit the effectiveness of flu vaccines, say researchers who tested blood samples from immunized people of various weights over a year.

In Tuesday's issue of the International Journal of Obesity, U.S. scientists looked at immune responses to the influenza vaccine after one month and 12 months after the jab among 499 healthy weight, overweight and obese adults who were vaccinated during the 2009 H1N1 pandemic.

Obesity itself is known to be a risk factor for influenza, but this study was the first to look at the effects of obesity and flu vaccinations using blood samples.

"What we found was although they made an initial antibody response to the flu vaccine similar to healthy weight people, they weren't able to maintain it to the same degree as healthy weight individuals," the study's lead author, Melinda Beck, a professor at the University of North Carolina at Chapel Hill’s Gillings School of Global Public Health, said in an interview with CBC News.

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Specifically, about half of obese participants had a four-fold decrease in antibody levels at 12 months compared to one month post vaccination. In comparison, less than a quarter of healthy weight participants had a four-fold decrease in antibody levels.

The results suggest that if someone who is obese is vaccinated early in the year then their antibody levels may decline during flu season, which runs from October to April in the Northern Hemisphere. If so, they may be more susceptible to flu.

Sicker from flu?

In laboratory experiments,  the researchers also found that samples from obese participants had a worse response in their CD8+ T cells — a type of white blood cell that plays a key role in the body's immune system — compared with people of a healthy weight.

That suggests overweight and obese people are more likely to become sicker and have more complications.

"That's because influenza-specific CD8+ T cells do not protect against infection, but instead act to limit the disease's progression and severity," said Heather Paich, a doctoral student in Beck's lab.

The study had limitations. Investigators only looked at blood samples from a small group. The participants were never actually examined.

Also, since the researchers only checked immune responses twice after vaccination, they aren’t able to say when the immune response drops off.

They hope to do follow-up studies to investigate that, as well as to see why it might be happening.

Other researchers have seen a decline in immune response to tetanus shots and hepatitis B vaccine among people who are obese, said CBC medical specialist Dr. Karl Kabasele.

Kabasele recommends that everyone get a flu shot, regardless of their weight.

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