Randomized, placebo-controlled phase 3 trial evaluating safety, immunogenicity, and reactogenicity of RSVPreF3-Mat in high-risk pregnant women and their infants.
Zourab Bebia, Ilse Dieussaert, Lisa Jose et al.
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In 30 seconds
This phase 3 randomized, placebo-controlled trial assessed RSVPreF3-Mat safety, reactogenicity, and immunogenicity in high-risk pregnant women and their infants. Enrollment was stopped and the study unblinded after a separate trial in healthy pregnant women observed an increased risk of preterm birth associated with the vaccine. Among 169 maternal participants, preterm birth occurred in 18.2% of the vaccine group and 19.7% of the placebo group; one neonatal death occurred in each group. Vaccination increased maternal RSV antibody levels, with evidence of placental transfer to infants.
Key findings
- Preterm birth occurred in 18.2% of vaccine recipients and 19.7% of placebo recipients; one neonatal death occurred in each group.
- At delivery, maternal neutralizing antibody titers were 8.87-fold higher for RSV A and 8.21-fold higher for RSV B than before vaccination.
- RSVPreF3-specific IgG was 14.12-fold higher at delivery than before vaccination; the placental transfer ratio was 1.33.
- No serious adverse events in maternal or infant participants were considered vaccine-related.
Why it matters
Maternal vaccination may provide infants with RSV antibodies through placental transfer, and this trial documents substantial antibody responses in a high-risk pregnancy population. Safety findings should be interpreted alongside the early study termination prompted by a preterm-birth signal in a separate trial. The results therefore contribute immunogenicity and safety data but do not resolve the broader safety concern.
What to keep in mind
Enrollment was stopped early and the study unblinded after a preterm-birth risk was observed in another trial, limiting the evidence available from this study.