medwireNews: Maternal vaccination reduces the likelihood of medically attended influenza illness by a third in infants younger than 6 months, with maximum effectiveness observed in infants under 3 months and those born to mothers vaccinated during the third trimester, indicate findings from a study published in JAMA Pediatrics.
The case–control study collated information for 3764 infants aged younger than 6 months who were recorded in the New Vaccine Surveillance Network as having been admitted to one of seven US pediatric institutions for fever or respiratory symptoms between the 2016–2017 and the 2019–2020 influenza seasons. Of these infants, 223 had a confirmed diagnosis of influenza and 3541 infants tested negative for influenza.
Leila Sahni (Baylor College of Medicine and Texas Children’s Hospital, Houston, USA) and colleagues report that 53% of the mothers in the study were vaccinated at least 2 weeks before delivery.
Among infants younger than 6 months, the vaccine exhibited an overall effectiveness of 34%, after adjusting for infant age, hospital site, and date, and this effectiveness increased to 53% for infants younger than 3 months, prompting the authors to say that “maternal influenza vaccination during pregnancy provided important protection for the infant in the first few months of life before infants are eligible for vaccination.”
The rate of vaccine effectiveness was 39% for prevention of hospital admission and 19% for prevention of emergency department visits, they add.
Vaccination was 52% effective for infants born to mothers vaccinated in the third trimester but just 17% effective when mothers were vaccinated in the first or second trimester. Further, the effectiveness was higher in infants born to mothers who received current season vaccination compared with the prior season’s vaccine (42 vs 34%), observe the researchers.
The authors explain that antigenic drift in circulating influenza viruses between the 2015–2016 and 2019–2020 influenza seasons led to A/H3N2 virus predominance in 2017–2018 and 2018–2019 and a mismatch between influenza and vaccine antigenic profiles that resulted in low vaccination effectiveness. After excluding A/H3N2-related illness, the point estimate of effectiveness increased from 34% to 43%, they say, supporting “the need for more immunogenic vaccines against A/H32N2 viruses” to confer better protection to mothers and infants.
They conclude that “[w]hile continued efforts are needed to determine optimal timing, clinicians should continue to offer influenza vaccination at any time during pregnancy to protect both the pregnant person and infant” considering the “well-documented benefits of maternal influenza vaccination for both mothers and infants.”
In a related editorial, Katherine Poehling and co-workers, from Wake Forest School of Medicine in Winston-Salem, North Carolina, USA, discuss the difficulties of the timing of influenza vaccination in pregnancy and acknowledge the need to balance the benefit to the pregnant individual, who ideally should be vaccinated early for pregnancy-related protection, and the infant, who may have higher transplacental antibody levels with later administration.
They also highlight the need to eliminate racial and ethnic disparities in vaccine uptake to achieve optimal outcomes for minority populations as well.
The editorialists conclude: “Our patients need us to advocate for universal vaccine registries and roll up our sleeves and work collaboratively to optimize maternal and infant health for all.”
medwireNews is an independent medical news service provided by Springer Healthcare Ltd. © 2024 Springer Healthcare Ltd, part of the Springer Nature Group.
JAMA Pediatr 2023; doi:10.1001/jamapediatrics.2023.5639
JAMA Pediatr 2023; doi:10.1001/jamapediatrics.2023.5630