June 6 (UPI) -- Researchers at the University of North Carolina at Chapel Hill found that obesity may negatively impact the effectiveness of the influenza vaccine.
The study showed that obese adults in the United States who get the flu vaccine are twice as likely to get the flu compared to healthy weight individuals.
Obesity, along with age, pregnancy and certain chronic conditions increase a person's risk of dying from the flu.
"Vaccinated obese adults are twice as likely to develop influenza and influenza-like illnesses compared to vaccinated healthy weight adults," Melinda Beck, researcher at the University of North Carolina at Chapel Hill, said in a press release.
Researchers compared 1,022 adults from North Carolina -- categorized as healthy, overweight or obese -- who received a flu vaccine during the 2013-2014 and 2014-2015 flu seasons. Those researchers found that 9.8 percent of obese participants had confirmed a flu or flu-like illness, compared to 5.1 percent of those in healthy weight category.
Serum samples were taken from participants before and after they received their influenza shots. Those samples were compared with the antibody levels of vaccinated participants who got the flu despite receiving the vaccination.
The samples were tested using the Hemaglutination Inhibition Assay, or HAI, a widely-used test that shows how many antibodies have built up in the body to fight infections like the flu.
The serum sample testing showed no differences in the antibody counts between vaccinated participants who did not get the flu and those who did, or between obese participants and healthy weight participants.
This contradicts the current standard blood testing that is used to show whether a person has enough antibody protection against the flu or not, suggesting that the effectiveness of influenza vaccines should be reassessed for use in obese adults.
Researchers believe the reason more obese patients got the flu is that the T cells, which support the protection and recovery from influenza, people do not function properly in obese individuals.
"Impaired cell functioning, despite the robust production of antibodies, may make vaccinated obese adults more susceptible to influenza infection," Scott Neidich, lead study author, said. "Alternative approaches may be needed to protect obese adults from both seasonal and pandemic influenza virus infections."
The study was published June 6 in the International Journal of Obesity.