Why To Exercise Today: So Your Flu Shot Works

Researchers studied 74 people given the combination vaccine against three strains of flu in the 2009-10 season, measuring their antibody response one month after getting the shot and then a year later. A third of the group were of normal weight, a third overweight and a third obese. Most were women.

After one month, overweight people had produced about the same level of antibodies as those of normal weight. But 11 months later, more than half of the obese patients had a fourfold or greater decrease in antibodies, a drop seen in just 25 percent of the normal-weight subjects.

The study, published online last week in The International Journal of Obesity, found that the activity of CD8+ T cells, white blood cells that help fight flu infection, also decreased as body mass index increased.