Study: Obesity limits effectiveness of flu vaccines
Dr. Melinda Beck conducted research that
suggests that obesity might impair the human
body's ability to fight flu viruses.
People carrying extra pounds may need extra protection from
New research from the University of North Carolina at Chapel
Hill shows that obesity may make annual flu shots less
The findings, published online recently, in the International
Journal of Obesity, provide evidence explaining a phenomenon
that was noticed for the first time during the 2009 H1N1 flu
outbreak: that obesity is associated with an impaired immune
response to the influenza vaccination in humans.
These results suggest that overweight and obese people would be
more likely than healthy weight people to experience flu illness
following exposure to the flu virus," said Melinda Beck, PhD,
professor and associate chair of nutrition at the UNC Gillings
School of Global Public Health and senior author of the study.
"Previous studies have indicated the possibility that obesity
might impair the human body's ability to fight flu viruses.
These new findings seem to give us a reason why obese people
were more susceptible to influenza illness during the H1N1
pandemic compared to healthy weight people."
The study reports for the first time that influenza vaccine
antibody levels decline significantly in obese people compared
to healthy weight individuals. What's more, responses of CD8+ T
cells (a type of white blood cell that plays a key role in the
body's immune system) are defective in heavier people.
Researchers studied people at a UNC clinic who had been
vaccinated in late 2009 with inactivated trivalent influenza
vaccine, the common flu vaccine for that fall and winter season.
Although obese, overweight and healthy weight individuals all
developed antibodies to flu viruses within the first month after
vaccination, the antibody levels in the blood declined more
rapidly in obese and overweight individuals over time.
About 50 percent of obese participants had a four-fold decrease
in antibody levels at 12 months compared to one month
post-vaccination. However, less than 25 percent of healthy
weight participants had a four-fold decrease in antibody levels.
Also, when study participants' blood samples were tested in the
lab and exposed to a flu virus 12 months after vaccination,
about 75 percent of healthy weight people's CD8+ T cells still
expressed interferon-γ, an infection-fighting protein. However,
only about 25 percent of obese patients' cells responded by
producing the protein.
When vaccination fails to prevent flu infection, people must
rely in part on their CD8+ T cells to limit the spread and
severity of infection, said Patricia Sheridan, PhD, research
assistant professor of nutrition and an author on the paper.
"If antibody titers are not maintained over time in the obese
individuals and memory CD+ T cell function is impaired, they may
be greater risk of becoming ill from influenza," Sheridan said.
Heather Paich, a doctoral student in Beck's lab, added: "The
findings also suggest 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 of disease."
In 2005, Beck and her colleagues reported that obesity in mice
impaired the animals' ability to fight influenza infections and
increased the percent dying from influenza, compared to lean
mice with the same infections. In 2010, her team showed that
obesity seemed to limit the mice's ability to develop immunity
to influenza, suggesting vaccines may not be as effective in
obese and overweight as in healthy weight humans. Also, the
fatality rate was higher in obese mice - none of the lean mice
died, but 25 percent of the obese mice died.
"This latest study shows that obese people may have a similar
impaired response to influenza vaccines as our mouse models did
to influenza virus," Beck said. "We need to continue to study
the effect of obesity on the ability to fight virus infections.
Influenza is a serious public health threat, killing up to half
a million people a year worldwide. As rates of obesity continue
to rise, the number of deaths from the flu could rise too. We
need to better understand this problem and to look for
Along with Beck, Sheridan and Paich, other UNC nutrition
department study authors are Erik A. Karlsson, now a
postdoctoral research associate at St. Jude Children's Research
Hospital, and Aileen B. Sammon and Lara Holland, who were
undergraduates at the time. Other authors are Michael G. Hudgens,
PhD, research associate professor of biostatistics in the public
health school; and Jean Handy, PhD, associate professor of
microbiology and immunology, Samuel Weir, MD, clinical associate
professor of family medicine, and Terry L. Noah, MD, professor
of pediatrics, all from the UNC School of Medicine.
More information and a copy of the study are available on the
-Story reprinted with permission of University of North Carolina
at Chapel Hill
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