Increased risk of influenza among vaccinated adults who are obese.

BACKGROUND: Influenza infects 5-15% of the global population each year, and obesity has been shown to be an independent risk factor for increased influenza-related complications including hospitalization and death. However, the risk of developing influenza or influenza-like illness (ILI) in a vaccinated obese adult population has not been addressed. OBJECTIVE: This study evaluated whether obesity was associated with increased risk of influenza and ILI among vaccinated adults. SUBJECTS AND METHODS: During the 2013-2014 and 2014-2015 influenza seasons, we recruited 1042 subjects to a prospective observational study of trivalent inactivated influenza vaccine (IIV3) in adults. A total of 1022 subjects completed the study. Assessments of relative risk for laboratory confirmed influenza and ILI were determined based on body mass index. Seroconversion and seroprotection rates were determined using prevaccination and 26-35 days post vaccination serum samples. Recruitment criteria for this study were adults 18 years of age and older receiving the seasonal trivalent inactivated influenza vaccine (IIV3) for the years 2013-2014 and 2014-2015. Exclusion criteria were immunosuppressive diseases, use of immunomodulatory or immunosuppressive drugs, acute febrile illness, history of Guillain-Barre syndrome, use of theophylline preparations or use of warfarin. RESULTS: Among obese, 9.8% had either confirmed influenza or influenza-like-illness compared with 5.1% of healthy weight participants. Compared with vaccinated healthy weight, obese participants had double the risk of developing influenza or ILI (relative risk=2.01, 95% CI 1.12, 3.60, P=0.020). Seroconversion or seroprotection rates were not different between healthy weight and obese adults with influenza or ILI. CONCLUSIONS: Despite robust serological responses, vaccinated obese adults are twice as likely to develop influenza and ILI compared with healthy weight adults. This finding challenges the current standard for correlates of protection, suggesting use of antibody titers to determine vaccine effectiveness in an obese population may provide misleading information.

Obesity is associated with impaired immune response to influenza vaccination in humans.

BACKGROUND: Obesity is an independent risk factor for morbidity and mortality from pandemic influenza H1N1. Influenza is a significant public health threat, killing an estimated 250,000-500,000 people worldwide each year. More than one in ten of the world's adult population is obese and more than two-thirds of the US adult population is overweight or obese. No studies have compared humoral or cellular immune responses to influenza vaccination in healthy weight, overweight and obese populations despite clear public health importance. OBJECTIVE: The study employed a convenience sample to determine the antibody response to the 2009-2010 inactivated trivalent influenza vaccine (TIV) in healthy weight, overweight and obese participants at 1 and 12 months post vaccination. In addition, activation of CD8⁺ T cells and expression of interferon-γ and granzyme B were measured in influenza-stimulated peripheral blood mononuclear cell (PBMC) cultures. RESULTS: Body mass index (BMI) correlated positively with higher initial fold increase in IgG antibodies detected by enzyme-linked immunosorbent assay to TIV, confirmed by HAI antibody in a subset study. However, 12 months post vaccination, higher BMI was associated with a greater decline in influenza antibody titers. PBMCs challenged ex vivo with vaccine strain virus, demonstrated that obese individuals had decreased CD8⁺ T-cell activation and decreased expression of functional proteins compared with healthy weight individuals. CONCLUSION: These results suggest obesity may impair the ability to mount a protective immune response to influenza virus.