GSK RSV Vaccine Safety in Pregnancy
The GSK RSV vaccine (RSVPreF3-Mat) is NOT currently approved for use in pregnancy and should NOT be administered to pregnant individuals due to safety concerns, specifically an increased risk of preterm birth identified in clinical trials. 1
Critical Safety Signal: Preterm Birth
The GSK maternal RSV vaccine candidate (RSVPreF3-Mat) underwent Phase 3 trials but enrollment was stopped early due to a significant safety signal:
- Preterm birth occurred in 6.8% of vaccinated mothers vs. 4.9% in placebo group (relative risk 1.37; 95% CI 1.08-1.74; P=0.01) 1
- Neonatal deaths were also numerically higher in the vaccine group (0.4% vs. 0.2%), likely attributable to the increased preterm births 1
- The trial failed to reach its target enrollment of 10,000 pregnant women because vaccination was halted 1
What IS Approved: Pfizer RSVpreF (Abrysvo)
The ONLY RSV vaccine currently FDA-approved and CDC-recommended for pregnancy is the Pfizer RSVpreF vaccine (Abrysvo), NOT the GSK vaccine. 2
Approved Specifications for Pfizer Vaccine:
- Timing: 32-36 weeks' gestation (32 weeks 0 days through 36 weeks 6 days) 2
- Seasonal administration: September through January in most of continental U.S. 2
- Single dose: One-time administration during pregnancy 2
Safety Profile of Pfizer Vaccine:
When restricted to the approved 32-36 week window, the Pfizer vaccine showed:
- Preterm birth: 4.2% (vaccine) vs. 3.7% (placebo) - not statistically significant 2
- Low birthweight: 4.1% vs. 3.4% - not statistically significant 2
- Neonatal jaundice: 6.3% vs. 6.7% - not statistically significant 2
The FDA determined that for the Pfizer vaccine at 32-36 weeks, benefits outweigh risks, including the potential (but not statistically significant) risk for preterm birth 2
Common Pitfalls to Avoid
- Do NOT confuse GSK and Pfizer RSV vaccines - they are different products with different safety profiles
- Do NOT administer before 32 weeks - earlier administration (24-36 weeks) showed higher preterm birth rates in trials 2
- Do NOT give outside seasonal window unless in jurisdictions with different RSV seasonality (Alaska, southern Florida, Hawaii, Puerto Rico, etc.) 2
Clinical Algorithm for RSV Prevention in Pregnancy
If patient is 32-36 weeks pregnant during September-January:
- Offer Pfizer RSVpreF (Abrysvo) vaccine
- Can be given simultaneously with Tdap, influenza, and COVID-19 vaccines 2
- Counsel about small numerical (but not statistically significant) increase in preterm birth risk
If patient declines or misses vaccination window:
- Infant should receive nirsevimab (monoclonal antibody) after birth 2
- Both maternal vaccine AND infant nirsevimab are not needed for most infants 2
Post-Marketing Surveillance Data
Real-world VAERS data for RSV vaccines in pregnancy (predominantly Pfizer, as GSK is not approved) shows:
- Preterm birth remains the most frequently reported pregnancy-specific adverse event (12.8% of reports) 3
- Median time from vaccination to preterm birth onset was 3 days 3
- Most preterm births were moderate to late (32 to <37 weeks) 3
- However, one recent cohort study from Argentina found vaccinated individuals had lower risk of preterm birth and low birthweight 4
The evidence remains mixed, requiring continued active surveillance, but current FDA and CDC guidance supports use of the Pfizer vaccine only at 32-36 weeks' gestation 2.