Association between body mass index and influenza antibody titer and immune cell count after influenza vaccination: an exploratory study.

BACKGROUND: Obesity is associated with altered immune function and may therefore influence the response to influenza vaccination. So, the objective was to investigate whether body mass index (BMI) affected influenza-specific antibody titers and immune cell counts after vaccination. METHODS: A subgroup of 25 participants from the MEGA cohort, a prospective observational study in Augsburg, Germany, aged 25-65 years, was analyzed, including 18 normal-weight individuals and 7 participants with obesity. Influenza antibody titers and immune cell phenotypes were assessed at four visits over nine months following vaccination. Differences between normal-weight and obese individuals were analyzed graphically using boxplots and tested using the Wilcoxon signed-rank test and the Mann-Whitney-U-test. RESULTS: At baseline, no significant differences in antibody titers were observed between BMI groups. Following vaccination, antibody titers increased in both groups and remained above pre-vaccination levels throughout follow-up. In the normal-weight group, the titers for all four analyzed antibodies differed significantly at every visit compared to visit 1. This was not the case in the obese group, where only the titers for the antibodies B/Colorado/06/2017 and B/Phuket/3073/2013 differed at the different visits in comparison to visit 1. Furthermore, obese participants showed a non-significant downward trend in Treg cell proportions over time; total T-cell counts did not demonstrate clear group-specific differences. B-cell proportions showed no consistent time trend, but significant within-group differences were observed between visits 1 and 4 in the normal-weight group and visits 1 and 2 in the obese group, with significant differences between groups at visits 1 and 3. CONCLUSION: The findings suggest that BMI may influence cellular immune responses after influenza vaccination, whereas antibody responses appeared broadly similar among BMI groups. Given the limited sample size these observations should be interpreted as exploratory. Larger studies are needed to clarify this relationship and to inform the development of tailored vaccination strategies for obese individuals.