A cohort study to assess the safety and coverage of COVID-19, influenza, and pertussis vaccine in Australian pregnant women.
TL;DR
Maternal influenza, pertussis, and COVID-19 vaccination were not associated with increased risks of hypertensive disorders, chorioamnionitis, premature rupture of membranes, antepartum or postpartum haemorrhage, small-for-gestational-age, or low birthweight, and neonatal outcomes were favourable.
Abstract
Background
The study aimed to evaluate the safety and impact of maternal influenza, pertussis, COVID-19 vaccine on perinatal outcomes and identify determinants of uptake among pregnant women in South Australia.
Methods
This retrospective cohort study included 19,098 pregnant women who delivered at the Women's and Children's Hospital in South Australia between 2020 to 2023. Cox proportional-hazards models estimated hazard ratios (HRs) for time-sensitive perinatal outcomes, and log-binomial models were used for time-independent outcomes. Poisson regression models were used to estimate adjusted prevalence ratios (aPRs) to identify factors influencing maternal vaccine uptake.
Results
Overall, 64.1% received influenza, 74.1% pertussis, and 29.5% received ≥1 COVID-19 dose during pregnancy. Maternal influenza, pertussis, and COVID-19 vaccination were not associated with increased risks of hypertensive disorders, chorioamnionitis, premature rupture of membranes, antepartum or postpartum haemorrhage, small-for-gestational-age, or low birthweight. Following maternal influenza vaccination, a 13% protective effect against preterm birth was observed, with similar reductions after pertussis (17% and nearly 50% fewer stillbirths) and COVID-19 vaccination (aHR 0.79, 95% CI 0.68-0.92). Both maternal influenza (aRR 0.94, 95% CI 0.91-0.98) and pertussis vaccination (aRR 0.89, 95% CI 0.86-0.92) were associated with a lower likelihood of experiencing at least one obstetric complication. A small increase in diagnosed gestational diabetes was observed among women vaccinated against influenza or pertussis. Neonatal outcomes were favourable, with lower rates of resuscitation, early-onset sepsis, and low Apgar scores among infants of vaccinated mothers. Younger, multiparous, unmarried, and First Nations women were less likely to be vaccinated, with lower uptake also observed among mothers whose infants were discharged to non-parental care.
Conclusions
Findings reaffirm the safety and added benefits of maternal influenza, pertussis, and COVID-19 immunisation, and highlight persistent inequities in uptake that require targeted, culturally safe strategies to ensure equitable protection for all pregnant women and their infants.