# 5922
Even in the earliest days of the 2009 H1N1 `swine’ flu outbreak, it was apparent that most people who contracted this novel virus experienced a relatively mild illness and recovered without incident.
There were exceptions, of course.
Some small percentage of people were hit hard by the pandemic H1N1 virus, with some experiencing ARDS (Acute Respiratory Distress Syndrome) and a few sustaining severe lung damage.
Thousands died, with most of those deaths occurring in those under the age of 65.
Many (but not all) of them had what was described as underlying `risk factors’; pregnancy, asthma, COPD, neurological disorders, heart failure, etc.
Extreme (or morbid) Obesity (BMI > 40) was one of the risk factors that emerged early in the 2009 outbreak, based primarily on anecdotal stories describing many of those admitted to intensive care units during the first wave of the illness.
The earliest mention I can find in this blog of the link to obesity (and smoking) came on May 25th, 2009; scarcely one month after the first swine flu cases were announced in San Diego (see H1N1 Morbidity And Previously Existing Conditions).
During 2009 obesity was often mentioned as a possible risk factor (see Obesity Seen As Major Risk Factor For Flu Complications) - then later - cautiously discounted as unproven (see More On The ACIP Meeting) in late July of 2009.
We saw more studies during 2010 that again raised the obesity question, and earlier this year in Extreme Obesity: A Novel Risk Factor For A Novel Flu we saw a study appearing in Clinical Infectious Diseases that found a three-fold increase in mortality among H1N1 patients who were morbidly obese.
Given the rising obesity rates in many countries around the world, an underlying risk factor that affects 25%-33% of the population is a pretty big deal.
All of which serves as prelude to a study that will appear later today in the International Journal of Obesity that looks at the immune response in those who are overweight, and finds significant differences from normal weight individuals.
This study found that while overweight people mounted a robust immune response from a flu vaccine during the first month after vaccination, within 12 months half saw a 4-fold decrease in antibody titers.
That’s twice the rate of normal weight individuals.
Furthermore, they found significant differences in the immune response of obese subjects that suggest they are not only more susceptible to influenza, but are also more likely to see severe disease or complications.
While the study is not yet online, we have the press release from the University of North Carolina School of Medicine. Follow the link to read it in its entirety.
Study: Obesity limits effectiveness of flu vaccines
Public release date: 25-Oct-2011
New research from the University of North Carolina at Chapel Hill shows that obesity may make annual flu shots less effective.
The findings, published online Oct. 25, 2011, in he 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, Ph.D., 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.
While the authors of this study can observe the decline in antibody response in the obese, the reasons behind it are less clear. They state:
"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 solutions."
Just as we’ve seen with those over 65 (see Study: Flu Vaccines And The Elderly and Flu Shots For The Elderly May Have Limited Benefits), those who are most at risk from influenza often see a reduced benefit from the current vaccine.
That isn’t to dismiss the flu vaccine as useless or a waste of time for these higher risk groups. Some protection is undoubtedly better than none.
But it is further evidence of the need to develop better flu shots that can help protect everyone.
Particularly those who mount a less-than-robust immune response to vaccines today.
