Maternal Vaccination Protects Infants Against Flu and Pertussis

Abstract

Source: Rowe SL, Leder K, Perrett KP, et al. Maternal vaccination and infant influenza and pertussis. Pediatrics. 2021;148(3): e2021051076; doi.10.1542/peds.2021-051076Investigators from multiple institutions in Australia conducted a population-level inception cohort study to assess the effectiveness of maternal influenza and pertussis vaccination during pregnancy in preventing these diseases in their children during the first 6 months of life. For the study, they abstracted data from the Victorian Perinatal Data Collection (VPDC) on women whose pregnancies ended between September 2015 and December 2017. The VPDC includes information on all live births and stillbirths in Victoria, Australia, including demographic and clinical data related to pregnancy and birth. In addition, whether the mother received influenza and/or pertussis vaccine at any time during pregnancy is recorded. Data from multiple databases were reviewed to identify laboratory-confirmed cases of influenza and pertussis in infants <6 months old during the study period and record ED visits, hospital admissions, and deaths from influenza and pertussis. Information from these databases and VPDC were linked to identify mother-infant dyads.The primary study outcomes were laboratory-confirmed cases of influenza and pertussis in infants born to mothers included in the study, and secondary outcomes included cases of severe disease, defined as ED visit, hospitalization, or death from influenza or pertussis in study infants. Poisson regression was used to calculate the relative risk (RR) for influenza and pertussis in infants of mothers vaccinated during pregnancy vs not vaccinated, after adjusting for multiple confounders. Results were stratified in infants <2 months old, and those 2 to <6 months of age. Vaccine effectiveness (VE) of maternal immunization in preventing childhood illness was estimated as (1-RR) × 100.Data were analyzed on 186,962 mother-infant dyads. Overall, 45.9% of study women were vaccinated against influenza during pregnancy and 68.5% against pertussis. There were 185,404 and 184,194 infants, respectively, included in influenza and pertussis vaccination analyzes. The risk of influenza was significantly reduced in children whose mothers were vaccinated, both among children <2 months old (RR, 0.44; 95% CI, 0.25, 0.77), and in those 2 to <6 months of age (RR, 0.64; 95% CI, 0.42, 0.98), with VE estimated as 56.1% (95% CI, 23.3%, 74.9%) and 35.7% (95% CI, 2.2%, 57.7%), respectively. Maternal vaccination reduced the risk of pertussis in infants <2 months old (RR, 0.20; 95% CI, 0.06, 0.63), with an estimated VE of 80.1% (95% CI, 37.1%, 93.7%), but no significant effect was noted among infants 2 to <6 months old (RR, 0.68; 95% CI, 0.33, 1.39). Maternal pertussis immunization reduced the risk of severe pertussis in infants <2 months old (RR, 0.38; 95% CI, 0.16, 0.94). There were no significant effects from maternal vaccination on severe cases of pertussis in children 2 to <6 months old or on influenza among children <6 months old.The authors conclude that maternal vaccination during pregnancy reduces the risk of influenza and pertussis in infants <2 months old.Dr Brady has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.The goal of maternal immunization is to provide infants with passive antibodies prior to their first dose of vaccines. In a previous study, Baxter et al1 noted that maternal Tdap during pregnancy significantly reduced pertussis risk during the entire first year of life (See AAP Grand Rounds. 2017;38[2]:15.)1 In the current study, which included infants born at ≥30 weeks’ gestation, this benefit was most notable only in infants <2 months. In contrast, Baxter et al1 enrolled only infants born at ≥37 weeks’ gestation, allowing more time for antibody transfer after maternal Tdap receipt (usually between 27–36 weeks’ gestation).2As demonstrated by the results of the current study, maternal vaccination during pregnancy also reduces the infant’s risk for influenza during the first 6 months of life. Tdap and influenza vaccination rates during pregnancy, however, remain suboptimal.3 To assess influenza and Tdap vaccination coverage among women pregnant during the 2020–21 influenza season, the Centers for Disease Control and Prevention (CDC) conducted a survey during April 2021.4 Among 1,795 survey respondents who were pregnant anytime during October 2020–January 2021, 54.5% reported receiving an influenza vaccine before or during pregnancy. Among 729 respondents, 53.5% reported receiving Tdap during pregnancy. Unfortunately, receipt of both influenza and Tdap vaccines was reported by only 30.7% of women.COVID-19 vaccines also are recommended for all pregnant women.5 Providers need to take every opportunity to recommend these vaccines for their pregnant patients.Vaccination of pregnant women with Tdap, influenza, and COVID-19 vaccines is safe and protects the mother and her young infant.As influenza vaccines are approved only for infants ≥6 months of age, the 6-month duration of immunity conferred by maternal influenza vaccination provides further support for maternal immunization.