The Impact of Obesity on Influenza Vaccine Immunogenicity and Antibody Transfer to the Infant During Pregnancy.

BACKGROUND/OBJECTIVES: Influenza vaccination is recommended for pregnant women, offering the dual benefit of protecting pregnant women and their newborn infants against influenza. This study aimed to investigate the impact of body mass index (BMI) on influenza vaccine responses in pregnant women and their newborns.

METHODS

Participants included pregnant women attending the Women's and Children's Hospital in South Australia between 2018 and 2021. Maternal blood samples were collected prior to and at 1 and 6 months post-influenza vaccination to measure antibody responses by hemagglutination inhibition (HI) assay. Cord blood samples were also collected. The percentages of participants achieving HI titre ≥40 were compared between obese and non-obese groups.

RESULTS

A total of 73 women were enrolled and received quadrivalent influenza vaccination at a mean age of 32 years (range 21-44 y) and median gestation of 24 weeks (range 11-37 weeks). BMI at vaccination was ≥30 kg/m for 21/73 women (29%). Most pregnant women demonstrated antibody titres ≥ 40 to all four influenza vaccine strains at 1 month post-vaccination regardless of BMI category (BMI ≥ 30 kg/m: 19/20; 95% vs. BMI < 30 kg/m: 47/49; 96%). At 6 months post-vaccination, 12/17 (71%) obese women compared to 36/43 (84%) non-obese women ( = 0.25) maintained HI titres ≥ 40. Cord blood serology showed HI titres ≥ 40 for 11/17 (65%) infants born to mothers with BMI ≥ 30 compared to 30/35 (86%) infants delivered by mothers with BMI < 30 kg/m.

CONCLUSIONS

A high BMI did not impair influenza vaccine antibody responses in pregnant women at 1 month post-vaccination. However, at 6 months post-vaccination, and in the cord blood samples, the percentages maintaining HI titre ≥ 40 were lower for obese women than for non-obese pregnant women.