Abstract
BackgroundAlthough pregnant women are a priority group for influenza vaccination, its effect on birth outcomes has long been debated. Numerous observational studies and a few randomized controlled studies have been conducted, with inconsistent results.ObjectivesTo evaluate the association of influenza vaccination in pregnancy with adverse birth outcomes.Data sourceThe Cochrane Library, PubMed, EMBASE, Web of Science, and Scopus were searched.Study eligibility criteriaThis analysis included randomized placebo-controlled studies, cohort studies, and case-control studies, in which inactivated influenza vaccination was given during pregnancy and fetal adverse birth outcomes were assessed.Participants & interventionWomen who received inactivated influenza vaccine during pregnancy and their offspring.Study appraisal and synthesisTwo independent reviewers and a third reviewer collaborated in study selection and data extraction. A Bayesian 3-level random-effects model was utilized to assess the impact of maternal influenza vaccination on birth outcomes, which were presented as odds ratios (ORs) with 95% credible interval (CrIs). Bayesian outcome probabilities (P) of an OR<1 were calculated, and values of at least 90% (0.9) were deemed to indicate a significant result.ResultsAmong the 6,249 identified publications, 48 studies were eligible for the meta-analysis, including 2 randomized controlled trials, 41 cohort studies, and 5 case-control studies. The risk of none of the following adverse birth outcomes decreased significantly: preterm birth (OR = 0.945, 95% CrI: 0.736–1.345, P = 73.3%), low birth weight (OR = 0.928, 95% CrI: 0.432–2.112, P = 76.7%), small for gestational age (OR = 0.971, 95% CrI: 0.249–4.217,P = 63.3%), congenital malformation (OR = 1.026, 95% CrI: 0.687–1.600, P = 38.0%), and fetal death (OR = 0.942, 95% CrI: 0.560–1.954, P = 61.6%). Summary estimates including only cohort studies showed significantly decreased risks for preterm birth, small for gestational age and fetal death. However, after adjusting for season at the time of vaccination and countries’ income level, only fetal death remained significant.ConclusionThis Bayesian meta-analysis did not find a protective effect of maternal influenza vaccination against adverse birth outcomes, as reported in previous studies. In fact, our results showed evidence of null associations between maternal influenza vaccination and adverse birth outcomes.
Highlights
Pregnant women are deemed vulnerable to severe complications from influenza infection due to changes in the immune system and heart and lung function during pregnancy [1]
After adjusting for season at the time of vaccination and countries’ income level, only fetal death remained significant. This Bayesian meta-analysis did not find a protective effect of maternal influenza vaccination against adverse birth outcomes, as reported in previous studies
The inclusion criteria were 1) human studies; 2) inactivated influenza vaccination given in any period of pregnancy; 3) reporting the target outcomes of preterm birth (PTB), low birth weight (LBW), small for gestational age (SGA), fetal death, and congenital malformations; 4) randomized controlled trials (RCTs), prospective or retrospective cohort studies, case-control studies; 5) placebo-controlled studies, and 6) the availability of full-text published articles in the English language
Summary
Pregnant women are deemed vulnerable to severe complications from influenza infection due to changes in the immune system and heart and lung function during pregnancy [1]. Based on the evidence of the landmark Mother’s Gift trial in Bangladesh [4], the World Health Organization (WHO) Strategic Advisory Group for Experts on Immunization recommended in 2012 that pregnant women be considered a priority group for influenza vaccination [5]. The two-fold benefit of inactivated influenza vaccine in preventing laboratory-confirmed influenza infection, both in pregnant women and infants, is convincing [9, 10], especially as it has been proven in recent, large-scale, phase 4 randomized controlled trials (RCTs) conducted in Mali [11], Nepal [12], and South Africa [10, 13]. Pregnant women are a priority group for influenza vaccination, its effect on birth outcomes has long been debated. Numerous observational studies and a few randomized controlled studies have been conducted, with inconsistent results
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