Influenza is a global problem that affects up to 10% of adults and 30% of children worldwide. The flu is responsible for 500,000 deaths annually and even more during influenza pandemics. The elderly, the young, and individuals with chronic diseases (like asthma and COPD) are most at risk for extended illness and mortality from the flu. To combat this large global problem, a seasonal vaccine is released (free in most countries) that is designed to vaccinate against the 3 or 4 most prevalent strains for that season. There is no universal vaccine for the flu available yet because of the high mutation rate of the virus that makes it different from year to year. Getting the annual flu vaccine is our most effective tool for fighting this infection and it is often given to the sick, elderly, and young first. We assume that the vaccine is effective in all people who receive it but don’t currently have data on whether something like obesity might alter the effectiveness of the vaccine. This is what a team of researchers from North Carolina have decided to investigate.
Published in the International Journal of Obesity, the team recruited 1022 subjects from 2013-2014 and 2014-2015 undergoing vaccination against the flu and set out to determine whether BMI (measure of obesity) influenced the effectiveness of the vaccine. They characterized the number of confirmed influenza infections and suspected infections in each person and then separated them into groups dependent on their BMI. Among individuals who received the vaccine, 5.1% of healthy weight people had a confirmed or suspected influenza infection where as 9.8% of obese individuals were infected. This translated to a 2-fold increase in risk for contracting influenza even after vaccination. There was a trend towards an increased risk in individuals who were overweight but not obese but this didn’t reach significance likely due to the small number of participants. The increase in risk was present even though the participants had seemingly strong immune responses to the vaccine.
The first question that comes up with these results is whether in obese individuals that vaccine fails to protect them because it fails to set up immunity. The researchers found this not to be the case in their samples when they looked for antibodies against the strains of influenza in the vaccine. This means that even though the obese individuals mount an appropriate response to the initial vaccine they don’t seem to be able to fight off the infection. This brings up a second question. Are obese individuals more susceptible to influenza infections with or without the vaccine simply because of low levels of inflammation in their body brought on by their obesity? Or are the immune cells from their body (namely the T cells) not functioning properly and therefore weakening the ability of the body to fight the flu despite the vaccine? This seems most plausible as there is evidence showing the obesity is related to a reduction in the effectiveness of T-cells in fighting off infections.
More work needs to be done but the rising epidemic of obesity worldwide may make influenza pandemics worse in the coming years. Understanding why obese people are less protected by the vaccine will allow us to develop better vaccines or treatment options to help them fight the flu.
Image Credit: Flickr William Brawley