Abstract
ABSTRACT Vaccination against influenza during pregnancy provides direct protection to pregnant women and indirect protection to their infants. Trivalent inactivated influenza vaccines (IIV3s) are safe and effective during pregnancy, but quadrivalent inactivated influenza vaccines (IIV4s) have not been evaluated in pregnant women and their infants. Here, we report the results of a randomized phase IV study to evaluate the immunogenicity and safety of IIV4 vs. IIV3 in pregnant women. Participants aged ≥18 years at weeks 20 to 32 of gestation were randomly assigned in a 2:1 ratio to receive a single dose of IIV4 (n = 230) or IIV3 (n = 116). Between baseline and 21 days after vaccination, hemagglutination inhibition (HAI) antibody titers increased in both groups by similar magnitudes for the two influenza A strains and single B strain common to IIV4 and IIV3. For the additional B strain in IIV4, HAI titers were higher in IIV4 recipients than IIV3 recipients (post-/pre-vaccination geometric mean titer ratio, 6.3 [95% CI: 5.1 − 7.7] vs. 3.4 [95% CI: 2.7 − 4.3]). At delivery, in both groups, HAI antibody titers for all strains were 1.5 − 1.9-fold higher in umbilical cord blood than in maternal blood, confirming active transplacental antibody transfer. Rates of solicited and unsolicited vaccine-related adverse events in mothers were similar between the two groups. Live births were reported for all participants and there were no vaccine-related adverse events in newborns. These results suggest IIV4 is as safe and immunogenic as IIV3 in pregnant women, and that maternal immunization with IIV4 should protect newborns against influenza via passively acquired antibodies.
Highlights
Pregnant women and young infants are among the population subgroups at greatest risk of severe illness, complications, and death from influenza.[1,2] Hospital admissions for influenza illness are more frequent among pregnant women than nonpregnant women,[3,4] and influenza in young infants frequently leads to hospitalization,[5] bacterial co-infections,[6,7] and a higher mortality rate than in older children.[8]
The study ended on June 14, 2018 and was completed by all subjects except for two vaccinated with quadrivalent inactivated influenza vaccine (IIV4) and one vaccinated with trivalent inactivated influenza vaccine (IIV3)
Subject demographics were similar between the two groups: the median age was 32.1 years for the women vaccinated with IIV4 and 30.7 years for those vaccinated with IIV3, and the median gestational age at enrollment was 25 weeks for the IIV4 recipients and 24 weeks (IQR: 21 − 27 weeks) for the IIV3 recipients
Summary
Pregnant women and young infants are among the population subgroups at greatest risk of severe illness, complications, and death from influenza.[1,2] Hospital admissions for influenza illness are more frequent among pregnant women than nonpregnant women,[3,4] and influenza in young infants frequently leads to hospitalization,[5] bacterial co-infections,[6,7] and a higher mortality rate than in older children.[8]. The World Health Organization (WHO)[1] and other advisory bodies[10,11,12] recommend that pregnant women are prioritized for influenza vaccination, since this provides both direct protection to pregnant women and indirect protection to their infants via transplacental maternal antibody transfer.[2,13,14,15,16] This strategy is especially important for preventing influenza illness in infants aged less than 6 months because influenza vaccines are not licensed for use in this age group
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