Obesity doesn’t hamper flu vaccine response in pregnancy

LJUBLJANA, SLOVENIA – A high body mass index in pregnant women who receive a seasonal influenza vaccine doesn’t impair their vaccine response; indeed, it might actually improve their seroconversion rate, Michelle Clarke reported at the annual meeting of the European Society for Paediatric Infectious Diseases.

^{Bruce Jancin/MDedge News}

Michelle Clarke

She presented a prospective cohort study of 90 women vaccinated against influenza during pregnancy, 24 of whom had a BMI of 30 kg/m² or more. The impetus for the study was the investigators’ understanding that influenza in pregnancy carries an increased risk of severe complications, obesity is a known risk factor for more severe episodes of influenza, and vaccine responses could potentially be adversely affected by obesity, either because of the associated inflammatory state and altered cytokine profile or inadequate vaccine delivery via the intramuscular route. Yet the impact of obesity on vaccine responses in pregnancy has been unclear.

Blood samples obtained before and 1 month after vaccination showed similarly high-titer postvaccination seropositivity rates against influenza B, H3N2, and H1N1 regardless of the women’s weight status. Indeed, the seropositivity rate against all three influenza viruses was higher in the obese subgroup, by a margin of 92%-74%. Also, postvaccination geometric mean antibody titers were significantly higher in the obese group. Particularly impressive was the difference in H1N1 seroconversion, defined as a fourfold increase in titer 28 days after vaccination: 79% versus 55%, noted Ms. Clarke of the University of Adelaide.

Of note, influenza vaccination in the first trimester resulted in a significantly lower seropositive antibody rate than vaccination in the second or third trimesters. The implication is that gestational age at vaccination, regardless of BMI, may be an important determinant of optimal vaccine protection for mothers and their newborns. However, this tentative conclusion requires confirmation in an independent larger sample, because the patient numbers in the study were small: Seropositive antibodies to all three vaccine antigens were documented in just 7 of 12 women (58%) vaccinated in the first trimester, compared with 47 of 53 (89%) vaccinated in the second trimester and 18 of 25 (72%) in the third.

Ms. Clarke reported having no financial conflicts regarding the study, which was supported by the Women’s and Children’s Hospital Research Foundation.

bjancin@mdedge.com