RSV Vaccine IS Safe in Pregnancy When Given at the Correct Gestational Age
The RSV vaccine (Pfizer RSVpreF) is safe and recommended for use in pregnancy when administered between 32-36 weeks' gestation, as the benefits of preventing severe infant RSV disease outweigh the potential risks. 1
Official Recommendations
The Advisory Committee on Immunization Practices (ACIP) and CDC recommend maternal RSV vaccination during pregnancy at 32-36 weeks' gestation to prevent RSV-associated lower respiratory tract disease in infants. 1, 2 This recommendation is based on large-scale clinical trials involving over 7,392 pregnant women that demonstrated both efficacy and an acceptable safety profile. 1
Safety Evidence and Key Nuances
The Preterm Birth Signal - Context Matters
The most important safety consideration involves preterm birth, but the data require careful interpretation:
In the approved dosing interval (32-36 weeks): Preterm birth occurred in 4.2% of vaccine recipients versus 3.7% of placebo recipients - a difference that was not statistically significant. 1, 2
In the broader trial dosing interval (24-36 weeks): Preterm birth rates were 5.7% versus 4.7%, also not statistically significant. 1
Critical detail: Among preterm births in the approved 32-36 week interval, 72% occurred at 36 weeks' gestation (late preterm), which carries substantially lower morbidity than earlier preterm birth. 2
ACIP explicitly judged that the benefits outweigh the potential risks for preterm birth and hypertensive disorders of pregnancy when the vaccine is given at 32-36 weeks. 1, 2
Other Safety Outcomes
Low birthweight and neonatal jaundice: No statistically significant differences were observed between vaccine and placebo groups. 1, 3, 4
Hypertensive disorders: Slightly more frequent in vaccine recipients (1.8% preeclampsia rate) but not statistically significant. 1
Common reactions: Injection site pain (40.6%), headache (31.0%), muscle pain (26.5%), and nausea (20.0%) - all mild to moderate. 1
The GSK Vaccine Story - Important Context
A different RSV vaccine candidate (GSK's RSVPreF3-Mat) had its trial stopped early due to a statistically significant increased risk of preterm birth (6.8% vs 4.9%, relative risk 1.37, P=0.01). 5 This vaccine is not approved and highlights why the Pfizer vaccine's narrower gestational age window (32-36 weeks vs GSK's 24-34 weeks) is critical for safety. 5
Efficacy - Why This Matters
The vaccine provides substantial protection when it matters most:
48.2% efficacy against RSV-associated lower respiratory tract infections in infants during the approved dosing interval. 1
Protection is highest in the first 3 months of life when infants are most vulnerable to severe RSV disease. 2, 3, 4
RSV causes 58,000-80,000 annual hospitalizations in U.S. children under 5 years, making it the leading cause of infant hospitalization. 2
Practical Implementation Algorithm
Confirm gestational age: Must be between 32 weeks 0 days and 36 weeks 6 days. 2, 4
Verify timing: Administer during September-January in most of the continental U.S. (adjust for Alaska, Hawaii, Puerto Rico, and other territories with different RSV seasonality). 1, 3, 4
Screen for contraindications: Exclude women at increased risk for preterm delivery (these patients were excluded from trials). 1
Co-administration is safe: Can give simultaneously with Tdap, influenza, and COVID-19 vaccines at different anatomic sites. 1, 3, 4
Document timing: If infant is born <14 days after maternal vaccination, the infant should receive nirsevimab as insufficient time exists for antibody transfer. 3, 4
Common Pitfalls to Avoid
Don't vaccinate before 32 weeks: The safety profile is less certain earlier in pregnancy, as demonstrated by the GSK trial. 2, 5
Don't vaccinate after 36 weeks: Insufficient time remains for antibody development and transplacental transfer (requires at least 14 days). 3, 4
Don't give both vaccine and nirsevimab to most infants: Either maternal vaccination OR infant nirsevimab is recommended, not both (exception: infants born <34 weeks should receive nirsevimab regardless of maternal vaccination status). 1, 2, 3, 4
Current data support only one lifetime dose: No evidence yet supports repeat vaccination in subsequent pregnancies. 1, 3, 4
Post-Marketing Surveillance
Early post-marketing data from VAERS (121 reports through June 2024) show adverse event patterns consistent with prelicensure studies, with preterm birth reported in 31% of reports and hypertensive disorders in 7%. 6 Ongoing studies continue to assess any potential association with preterm birth. 6