The impact of obesity on influenza Vaccine immunogenicity: A systematic review

Background: Influenza vaccines are important for reducing the burden of influenza, particularly for populations at risk of more severe infections. Obesity is associated with increased influenza severity and therefore individuals with obesity are often specifically recommended for annual influenza vaccination. Obesity is also associated with an altered inflammatory profile, which may influence vaccine responses. This systematic review aimed to evaluate the evidence for any association between obesity and influenza vaccine immunogenicity. Method(s): Studies reporting seroprotection (SP) and/or seroconversion (SC) for obese vs non-obese recipients following licensed influenza vaccination were included. PubMed, Embase and Scopus were searched, with the final search completed on 21 Feb 2025. The protocol was registered in PROSPERO. Study selection, data extraction and critical appraisal were conducted by two reviewers in Covidence. Meta-analysis was performed in S tata 17 using a random-effects model. Result(s): Of 2132 studies imported, 865 studies were screened and 140 underwent full-text review. Eleven studies reported outcomes for seroprotection and/or seroconversion for obese vs non-obese groups at 1-month following monovalent H1N1 (n = 1), trivalent (n = 6) or quadrivalent (n = 4) influenza vaccination. Studies included children (n = 5) and adults (n = 7) including pregnant women (n = 2). Study sample sizes varied from 44 to 1132 participants. Obesity was associated with a marginally higher likelihood of seroconversion or seroprotection for A/H1N1 (RR 1.04, 95 %CI 1.01-1.08; RR 1.08, 95 % CI 1.02-1.14) and marginally higher seroconversion for A/H3N2 strains (RR 1.11, 95 % CI 1.02-1.21). No significant differences were observed for Influenza B/Victoria and B/Yamagata strains. Conclusion(s): Obesity does not impair influenza vaccine immunity at one-month post-vaccination, and may enhance antibody responses, potentially due to a proinflammatory immune profile. Copyright © 2025