Obesity may increase the risk of contracting influenza and influenza-like illness (ILI), according to a study conducted by a team of investigators at the Human Vaccine Institute, Duke University, and at the University of North Carolina, Chapel Hill.

During the 2013-2014 and 2014-2015 influenza seasons, the researchers conducted a prospective observational study of trivalent inactivated influenza vaccine (IIV3) in 1042 adults (age 18 years or older). Individuals with immunosuppressive diseases, acute febrile illness, history of Guillain-Barre syndrome, those treated with immunomodulatory or immunosuppressive drugs, theophylline preparations, or warfarin, were excluded from the study.

The researchers assessed the relative risk for influenza and ILI on the basis of body mass index (BMI) and determined seroconversion and seroprotection rates using pre-vaccination and 26-35 day post-vaccination serum samples.

Obese individuals had considerably higher rates of either confirmed influenza or ILI, compared to healthy weight individuals (9.8% vs 5.1% respectively). Obese participants had double the risk of developing influenza or ILI, compared with vaccinated healthy weight individuals (relative risk=2.01, 95% CI 1.12, 3.60, P=0.020). Seroconversion and seroprotection rates did not differ between healthy weight and obese adults with influenza or ILI. 

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The researchers noted that obesity has been shown to be an independent risk factor for increased influenza-related complications, including hospitalization and death. The purpose of their study was to explore the risk of developing influenza or ILI in a vaccinated obese adult population.

They concluded that, “despite robust serological responses, vaccinated obese adults are twice as likely to develop influenza and ILI, compared to healthy weight adults.” Their finding has important implications because it “challenges the current standard for correlates of protection, suggesting the use of antibody titers to determine vaccine effectiveness in an obese population may provide misleading information.”


Neidich SD, Green WD, Rebeles J, Karlsson EA, Schultz-Cherry S, Noah TL, Chakladar S, Hudgens MG, Weir SS, Beck MA. Increased risk of influenza among vaccinated adults who are obese. Int J Obes (Lond). 2017 Jun 6. [Epub ahead of print]