Obese Individuals Respond Just as Well to Flu Vaccine

Daniel M. Keller, PhD

October 24, 2011

October 24, 2011 (Boston, Massachusetts) — It appears that body mass and obesity do not adversely affect the immune response to influenza vaccine. In fact, seroconversion to one component in the vaccine actually increased, Laura Coleman, PhD, RD, associate research scientist at the Epidemiology Research Center of the Marshfield Clinic Research Foundation in Wisconsin, reported during a poster session here at the Infectious Diseases Society of America (IDSA) 49th Annual Meeting.

During the 2009 H1N1 influenza pandemic, obesity was directly associated with complications and severity of disease. In vitro, obesity has been associated with reduced or altered function in several aspects of immunity. In addition, advancing age correlates with diminished immunocompetence and response. But Dr. Coleman said that no studies had compared the serologic response to influenza vaccine in obese and nonobese individuals.

Dr. Laura Coleman

She and her colleagues therefore tested the serologic response of adults 50 years of age and older, enrolled in September and October 2008, to trivalent influenza vaccine containing A/Brisbane/59/2007 (H1N1), A/Brisbane/10/2007 (H3N2), and B/Florida/4/2006 components. They collected blood samples before vaccination, 21 to 28 days after vaccination, and in April 2009. Through interviews or chart reviews, they also obtained information on demographics, comorbidities, immunomodulating medications, and height and weight to calculate body mass index (BMI).

Serum antibody levels were determined with hemagglutination inhibition assays. An assay titer of at least 1:40 was considered seroprotective, and a 4-fold increase in the assay from pre- to postvaccination was considered a seroconversion. Obesity was defined as a BMI of at least 30 kg/m2; individuals in the 18.5 to 24.99 kg/m2 range were deemed nonobese.

The study cohort, combining data from the Marshfield Clinic and from Vanderbilt University in Nashville, Tennessee, was roughly equally distributed across ages from 50 to 70-plus years, 60% female, 97% white, and had a mean BMI of 29.0 kg/m2 (40% of subjects had a BMI of 30 kg/m2 or higher). Prevaccination geometric mean titer (GMT) of antibody did not differ according to age or sex.

"We found that, in general, there was no difference in seroconversion or seroprotection rates or baseline antibody titers by BMI," Dr. Coleman told Medscape Medical News. "We found that obese individuals were just as likely to respond to the vaccine antigens as nonobese individuals." There was also no independent influence of comorbid conditions or sex on seroprotection or seroconversion.

With the odds ratio for the nonobese equal to 1, there was no statistically significant difference between the obese (n = 163) and nonobese (n = 250) people in the likelihood of seroconversion or seroprotection in response to the H1N1 vaccine component, nor was there any difference in the baseline GMT of antibody prevaccination or GMT fold increase postvaccination.

Similarly, the seroconversion, baseline GMT, and GMT fold increase were equivalent for both groups in response to the influenza B antigen. Seroprotection against the B subtype was not modeled because of the high proportion (94%) of subjects protected.

"There was one interesting and surprising finding, and that was that obese subjects actually had an increase in seroconversion to the H3N2 vaccine component. That is not the direction we would have expected to see an association," Dr. Coleman said.

The researchers do not know what to make of this finding, which was a modest association, with an odds ratio of 1.63 (95% confidence interval [CI], 1.04 to 2.55), for the obese group compared with the nonobese group. "It could have been something that occurred by chance, or it could be related to differences in leptin levels. We don't know," she said.

"Based only on this relatively small study, we do not see evidence for vaccine recommendations to be different for obese and nonobese individuals, at least not based on antibody response to the vaccine," she advised.

Andrew Pavia, MD, chief of pediatric infectious disease at the University of Utah in Salt Lake City, and chair of the Pandemic Influenza Task Force of the IDSA, told Medscape Medical News that the rationale for the study was a good one, because in the 2009 H1N1 influenza pandemic, obese people "were more likely to be hospitalized, more likely to end up in an intensive care unit, and more likely to die." It became clear that there needed to be more efforts to protect the morbidly obese from influenza and its consequences.

He said one problem is that it is harder to reach muscle with a standard needle when administering an intramuscular injection to an obese person. In the study, he said, "the immune response to vaccine was just as good in obese people as it was in people of normal body weight," but he cautioned that "these were trained investigators participating in the study, so their nurses used a standardized technique, and that assumes that they made extra efforts to give vaccine properly." He added that it would have been interesting to compare the antibody responses of obese and nonobese people who were vaccinated in the community to see if there were shortcomings among them in their antibody responses.

Nonetheless, he said, "I think this is a first step to providing some reassurance that vaccine works in the obese. I think the study probably bears confirmation, probably by looking at people vaccinated in the community. Ultimately, what you really want to look at is the efficacy against disease, so you'd like to see that you get the same 70% or 60% efficacy in an obese population that you get in a population of normal body mass in a year when the vaccine is pretty well matched [to the prevailing strains]."

Finally, he said, antibody titers are not a perfect predictor of protection, and obese people might have other issues that make them more susceptible, even if they have an equivalent level of antibody (e.g., decreased lung clearance or other metabolic effects of obesity).

There was no commercial funding for the study. Dr. Coleman and Dr. Pavia have disclosed no relevant financial relationships.

Infectious Diseases Society of America (IDSA) 49th Annual Meeting: Abstract 538. Presented October 21, 2011.

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.

processing....