Diet-Induced Obesity Dramatically Reduces the Efficacy of a 2009 Pandemic H1N1 Vaccine in a Mouse Model

Background. Obesity, a risk factor for increased severity of diverse diseases, is believed to have negative impact on vaccine efficacy. Recently, mortality has emerged as an outcome of pandemic influenza A virus subtype H1N1, necessitating development of effective vaccine strategies. Here we investigated effects of diet-induced obesity on vaccine-induced immune responses and protective efficacy against pandemic H1N1 influenza virus. Methods. Diet-induced obese and lean C57BL/6J mice were immunized with commercial monovalent 2009 H1N1 vaccine, and antigen-specific antibody responses and neutralizing activities were observed. Following vaccination, mice were challenged with homologous H1N1 virus, and pathogenesis and mortality were examined. Results. Vaccine-induced H1N1-specific antibody responses and neutralizing activities were markedly reduced in obese mice. Consistent with antibody responses, lung virus titers were significantly higher in obese mice than in lean controls after challenge. In addition, obese group showed greatly increased expression of proinflammatory cytokines and chemokines in lung tissue, severe lung inflammation, and higher eventual mortality rate (100%) compared with that among lean control mice (14%). Conclusions. Our results show that prophylactic immune responses and protectiveness induced by 2009 H1N1 vaccine could be extremely compromised in diet-induced obesity. These results suggest that novel vaccination strategies for high-risk groups, including the obese population, are required.