P1.204: Fetal safety of Influenza Vaccination in Pregnancy: Umbrella review and meta-analyses

Background: Although influenza vaccination during pregnancy is known to prevent seasonal flu outbreaks, reliable and contemporary quantitation of benefits and safety has not been performed. The aim of the current umbrella review to synthesize evidence from multiple meta-analyses was to reliably and robustly provide quantitative measures of the effectiveness and safety of influenza vaccines among gravidae.

Methods: We conducted a systematic search of PubMed, Scopus, Web of Science, and Embase from inception to 09/13/2023, including over 100 individual studies retaining 2.5 million pregnancies. Data were extracted from multiple meta-analyses and included studies were filtered to ensure no duplication within outcomes. Risk Ratios (RRs) and pooled proportions were calculated using R, with aggregate effect sizes and random-effects models applied. Egger’s test was used to assess publication bias. PROSPERO registration: CRD42024519189.

Results: Influenza vaccination during pregnancy resulted in a significant risk reduction of fetal death or stillbirth (RR 0.83 & 0.77, 95% CI 0.78-0.89 and 0.69-0.87), preterm birth (RR 0.92, 95%CI 0.88-0.96) and low birth weight neonates (RR 0.88, 95%CI 0.84-0.93). Reflective of changes in co-morbidities and other respiratory illness pandemics over the study interval, there was heterogeneity in some outcomes, such as preterm birth (I²: 63.06%), while other outcomes showed low to moderate heterogeneity. Egger’s test for publication bias indicated no significant bias across the studies.

Conclusion: Influenza vaccination during pregnancy is associated with significant and quantifiable reductions in the risk ratio of multiple adverse perinatal outcomes. Providing these quantitative estimates may aid in public health messaging and shared decision-making with patients and their families.