Multi-decade national cohort identifies adverse pregnancy and birth
outcomes associated with acute respiratory illness hospitalisations
during the influenza season
Abstract
Background: Despite the WHO recommendation that pregnant women be
prioritised for seasonal influenza vaccination, coverage in the Western
Pacific Region remains low. Our goal was to provide additional data for
the Western Pacific region about the value of maternal influenza
vaccination to pregnant women and their families. Methods: We conducted
a 16-year retrospective cohort to evaluate risks associated with
influenza-associated maternal acute respiratory infection (ARI) in New
Zealand. ARI hospitalisations during the May-September influenza season
were identified using select ICD-10-AM primary and secondary discharge
codes from chapter J00-J99 (diseases of the respiratory system). Cox
proportional hazards models were used to calculate crude and adjusted
hazard ratios (aHR) and 95% confidence intervals (CI). Results: We
identified 822,391 pregnancies among New Zealand residents between 2003
and 2018; 5,095 (0.6%) had >1 associated ARI
hospitalisation during the influenza season; these pregnancies were at
greater risk of preterm birth (aHR 1.5, 95% CI 1.3-1.7), and low
birthweight (aHR 1.7, 95% CI 1.5-2.0) than pregnancies without such
hospitalisations. We did not find an association between maternal ARI
hospitalisation and fetal death (aHR 1.1, 95% CI 0.6-1.4) during the
influenza season. Maternal influenza vaccination was associated with
reduced risk of preterm birth (aHR 0.8, 95% CI 0.7-0.9), and low
birthweight (aHR 0.9, 95%CI 0.8-0.9), and fetal death (aHR 0.5%, 95%
CI 0.3-0.7). Conclusion: In this population-based cohort, being
hospitalised for an ARI during the influenza season while pregnant was a
risk-factor for delivering a preterm or a low birthweight infant and
vaccination reduced this risk.