Flu Shot Less Effective in Obese or Overweight People

“That's exactly our hope — that we can find a vaccine that will work for everybody, but especially for these higher-risk populations.”


The U.S. Centers for Disease Control and Prevention (CDC) has been urging people to get their flu shot this season to stay away from catching the illness.

However, a study has found that flu vaccines are less effective for those who are obese or overweight. This could be a significant shortcoming considering that obesity affects over two-thirds of American adults.

Researchers have been studying why obese people do not respond well to the vaccine in order to develop better flu vaccines.

The finding became known during the flu pandemic in 2009 when the first major outbreak of the 21st century took place. Health authorities recognized that people who were overweight or obese were particularly more affected by the flu.

Infectious Disease Specialist Dr. Stacey Schultz-Cherry from St. Children’s Research Hospital said, “We had never seen that before. The virus is able to grow to higher [concentrations] and spread deeper in your lungs, which is not what you want during an influenza infection.”

Dr. Schultz-Cherry said this issue was raised at the University of Maryland. She said, “The students who were overweight/obese actually had more virus coming out in their exhaled breath.”

Another study found that people who were overweight shed the virus more when compared with people who had lower body weight.

“What’s particularly disturbing for us is the fact that the vaccine doesn’t work as well in this population,” said nutrition professor Melinda Beck from the University of North Carolina at Chapel Hill.

Beck examined two different parts of the immune system. The one that involves antibodies that can neutralize viruses and the other involves T-cells that combat diseases.

She said, “You usually think of the vaccine as protecting you with antibodies. And in fact, obese people could make a nice antibody response.”

Beck explained that obese or overweight people have altered metabolism over time, affecting many cells, including those immune cells that fight diseases.

Older people also have the same issues, she said. “Sometimes they can make an antibody response, but it’s their T cells that aren’t functioning, so they can still get infected with flu even though they’ve been vaccinated.”

Beck explained, “A 30-year-old obese person has the immune cells that look a lot like what you might expect in an 80-year-old individual.”

Therefore, researchers are leaving no stone unturned in bringing improvements in the vaccine that will people with obesity as well as older people.

Dr. Schultz-Cherry said, “That’s exactly our hope that we can find a vaccine that will work for everybody, but especially for these higher-risk populations.” The effort to improve flu vaccines would take years. Meanwhile, Dr. Schultz-Cherry said it is imperative for everybody to get vaccinated. She said, “There’s a lot of reasons to get the flu shot even if it doesn’t work as well as we want in this high-risk population.”