P1.199: Impact of Maternal RSV Vaccination during Pregnancy of Infant Outcomes: A Systematic Review and Meta-Analysis of RCTs

Background: Respiratory syncytial virus (RSV) continues to remain one of the leading causes of acute lower respiratory tract illness (LRTI) in children under 5 years. However, the disease burden is highest within the first 6 months of life. Furthermore, studies have reported that maternal RSV infection, especially during the third trimester, increases the risk of fetal complications, including prematurity, congenital anomalies, and respiratory and neurological illness. Maternal RSV vaccination is a promising preventive strategy of great interest, as it could have a substantial impact on infant RSV disease burden. We aim to comprehensively assess the impact of maternal RSV on clinical outcomes in infants.

Methods: Per PRISMA guidelines, a comprehensive review of studies from PubMed/MEDLINE, CENTRAL, EMBASE, clinicaltrials.gov, and WHO ICTRP (International Clinical Trials Registry Platform) was conducted for eligible RCTs (Randomized Controlled Trials) that reported on the impact of maternal RSV on infant outcomes. We utilized binary random-effects models to estimate pooled risk ratios (RR) and 95% confidence intervals (CI). Subgroup analyses, stratified by the RSV pre-F protein and RSV F protein vaccinations, were conducted to investigate their independent associations with the clinical outcomes. A p-value of ≤ 0.05 was deemed statistically significant.

Results: A total of six RCTs involving 17,991 pregnant women were included in our study. Regarding clinical outcomes, maternal RSV vaccination significantly reduced the risk of infant hospitalization due to RSV infection (RR 0.50; 95% CI 0.31-0.82; p=0.006) compared to placebo. However, no significant difference was seen in infant mortality (RR 0.81; 95% CI 0.36-1.81; p=0.60). Regarding adverse perinatal outcomes, maternal RSV vaccination with RSV pre-F protein vaccine was associated with a significant increase in pre-term births (RR 1.26; 95% CI 1.08-1.47; p=0.003). However, no significant difference was seen in congenital anomalies (RR 0.96; 95% CI 0.88-1.04; p=0.31).

Conclusion: Maternal RSV vaccination reduces hospitalizations due to RSV in infants. However, there are concerns about preterm birth in women receiving maternal RSV vaccination, particularly with the RSV pre-F protein subtype. Future research with an adequate sample size is required to establish the safety of maternal RSV vaccinations and draw definitive conclusions. Additionally, more studies are needed to evaluate the efficacy and safety of concurrent vaccinations during pregnancy, as multiple maternal vaccinations are generally recommended.