Maternal influenza vaccinations administered throughout the year significantly reduced influenza infections among infants and influenza-like illnesses in their mothers, in addition to reducing rates of low birth-weight, according to research published in The Lancet Infectious Diseases.
“An estimated 40% of the world’s population live in tropical zones, yet influenza vaccines are not widely used in this setting,” Mark C. Steinhoff, MD, director of the Global Health Center at Cincinnati Children’s Hospital Medical Center, and colleagues wrote. “Despite year-round circulation of influenza in tropical and subtropical regions, we are not aware of previous prospective or controlled randomized studies assessing year-round influenza immunization from Asia.”
Mark C. Steinhoff
To evaluate the safety and efficacy of year-round influenza maternal influenza immunization among mothers and infants residing in Nepal, the researchers conducted a phase 4, randomized, placebo-controlled trial in which two cohorts were enrolled consecutively in year-long sessions. The cohort included pregnant women from the Sarlahi district in southern Nepal who were married, aged between 15 and 40 years, 17 to 34 weeks pregnant at the time of enrollment and had not been vaccinated against influenza within the season.
Mothers were randomly assigned one to one to receive immunization or placebo, and were placed in blocks of eight, where they were further stratified by gestational age (17-25 weeks and 26-34 weeks). Throughout the study, researchers gathered serum samples before and after immunization alongside cord blood from a subset of women and infants. Staff who were collecting samples and making weekly visits from enrollment to 6 months after delivery were masked to the mother’s placement.
Steinhoff and colleagues also used PCR testing on midnasal swabs for respiratory viruses collected while mothers experienced acute febrile respiratory infections and while infants had any respiratory symptom. The incidence of maternal influenza-like illness during pregnancy and up to 180 days postpartum, low birth-weight and lab-confirmed influenza in infants up to 180 days post-birth were assessed.
The researchers enrolled 3,693 women (two cohorts: 1,041 placebo, 1,049 vaccine in first cohort; 805 placebo, 798 vaccine in second cohort) between April 25, 2011, and Sept. 9, 2013. Infants were also split into two cohorts, with 3,612 liveborn infants included (999 placebo, 1,010 vaccine in first cohort; 805 placebo, 798 vaccine in second cohort).
According to study results, maternal influenza immunization vaccine effectively reduced overall influenza-like illness among mothers by 19% (95% CI, 1-34) and reduced lab-confirmed influenza in infants aged younger than 6 months by 30% overall (95% CI, 5-48). Although the rate of “small-for-gestational-age infants” was not impacted by immunization, maternal vaccination was 15% effective at preventing low birth-weight (95% CI, 3-25).
Adverse events were comparable regardless of whether immunization was administered. Five mothers (0.3%) had a miscarriage in the vaccination groups, and 33 (1.8%) stillbirths occurred. Twenty (1.1%) infants were born with a congenital defect, and three mothers died in the vaccine group. Each group experienced comparable numbers of infant deaths, and no adverse events were associated with maternal immunization.
“The development of a child inside the mother affects that child its entire life, and low birth-weight has lifelong health implications for a child,” Steinhoff said in a press release. “The overall positive effect of performing these vaccinations — which is not expensive — is quite significant.” — by Katherine Bortz
Disclosure: Please see the study for a full list of relevant financial disclosures.