Flu shots less effective on obese patients: Researchers

By Sharon Kirkey, Postmedia News October 25, 2011

Obese people may face a higher risk of getting severely sick or dying from influenza because flu shots are less effective in the obese, U.S. researchers are reporting.

The study is the first to show that the antibodies produced in response to flu shots plunge dramatically in the obese compared to patients with healthy weights.

The researchers also found that obese people produce defective killer T-cells — cells that are vital in fighting infections.

The twin findings might explain why obese people were more likely to experience severe complications, hospitalizations and death during the H1N1 pandemic two years ago.

Even without a pandemic outbreak, influenza kills up to 500,000 people every year worldwide, the researchers write in the International Journal of Obesity.

What's more, "obesity is a growing health concern of epidemic proportions in many countries." In Canada, 24 per cent of adults are obese, according to Statistics Canada. As rates of obesity climb, deaths from flu could rise too, the researchers say.

Their study involved 499 healthy weight, overweight and obese adults who were vaccinated during the 2009 H1N1 pandemic. Blood samples were taken before the shots and then 30 days later so that the researchers could measure antibody levels. Their blood was checked again 12 months post-vaccination.

In an unexpected finding, obese people initially mounted a slightly more robust response to the shots than healthy weight people. But their antibody levels dropped far more rapidly over time.

At 12 months, more than 50 per cent of the obese patients experienced a four-fold plunge in antibody levels, compared to their one-month post vaccination.

Fewer than 25 per cent of healthy weight people showed the same drop over time.

Next, the researchers exposed the patients' blood samples to a flu virus in the lab 12 months after vaccination and checked their CD8 T cells — white blood cells that, if a person does get infected with flu, kill infected cells, clear the virus faster and lessen the severity of disease.

Obese people had fewer functional CD8 cells in response to influenza. About 75 per cent of healthy weight people's CD8 cells were still churning out infection-fighting proteins 12 months out, versus 25 per cent of obese people.

Flu season can run from October to April in the northern hemisphere, said first author Patricia Sheridan, a research assistant professor at the University of North Carolina at Chapel Hill. "If you get your vaccine early, if the antibodies decline you may not be protected" while flu is still circulating, she said.

The researchers don't know exactly when that large drop in antibodies to the flu shots occurred in the obese, or why it happens.

But "we have the first set of information to know that the vaccine response in obese people is different," Sheridan said.

Fat cells produce chemicals and toxins that impair the body's immune response, especially in cases of abdominal obesity, said Dr. David Lau, president of Obesity Canada and professor of medicine, biochemistry and molecular biology at the University of Calgary. For the immune-compromised flu can be lethal, which is why Lau says that it's even more important that obese people get vaccinated — even if obesity makes the shots less effective.

Should obese people get two flu shots? "Our data don't suggest that's a good idea," Sheridan said.

"For now, one vaccine is still the best option."

Other studies have shown that tetanus shots are less effective in obese children, and hepatitis B shots are less effective in obese adults.

skirkey@postmedia.com

source: Vancouver Sun