Is the Respiratory Syncytial Virus (RSV) vaccine safe for pregnant mothers?

Is the RSV Vaccine Safe for Pregnant Mothers?

Yes, the RSV vaccine (RSVpreF/Abrysvo) is safe for pregnant mothers when administered between 32 weeks 0 days and 36 weeks 6 days of gestation, with the FDA determining that benefits outweigh risks for preventing severe RSV disease in infants. 1, 2

FDA-Approved Safety Profile

The FDA approved RSVpreF vaccine in August 2023 with a specific safety warning about potential preterm birth risk, though this determination was based on non-statistically significant differences in clinical trials. 1

Key Safety Data from Clinical Trials

Preterm Birth Considerations:

• In the approved dosing interval (32-36 weeks), preterm births occurred in 4.2% of vaccine recipients versus 3.7% of placebo recipients—a difference that was not statistically significant 1, 2
• Most preterm births in the vaccine group occurred at 36 weeks' gestation, accounting for 72% of cases 2
• The FDA restricted administration to 32-36 weeks specifically to avoid potential preterm birth risk at <32 weeks' gestation, which carries significantly higher morbidity and mortality 1

Other Pregnancy Outcomes:

• Hypertensive disorders of pregnancy were observed more frequently in vaccine recipients compared to placebo, though differences were not statistically significant 1, 2
• Low birthweight occurred in 4.1% of vaccine recipients versus 3.4% of placebo recipients (not statistically significant) 1
• Neonatal jaundice rates were similar: 6.3% in vaccine group versus 6.7% in placebo group 1
• Congenital abnormalities showed no increased risk (RR 0.96,95% CI 0.88-1.04), with high-certainty evidence 3

Risk-Benefit Analysis

The FDA and CDC determined that vaccination benefits clearly outweigh potential risks when administered at the approved gestational window. 1, 2

Benefits Supporting Safety Determination:

• RSV causes 58,000-80,000 annual hospitalizations in children under 5 years, with infants <6 months at highest risk 2, 4
• Maternal vaccination reduces infant hospitalization with laboratory-confirmed RSV disease by 50% (RR 0.50,95% CI 0.31-0.82) 3
• Protection is highest during infants' most vulnerable first months of life when RSV disease burden is greatest 1

Maternal Safety Profile:

• Local injection-site reactions are common (40.7% versus 9.9% with placebo) but mild 5
• No increase in systemic reactions, fever, or serious adverse events in mothers 6
• One maternal death occurred in the vaccine group versus none in placebo across trials, but this difference may have little or no effect (RR 3.00,95% CI 0.12-73.50, low-certainty evidence) 3

Critical Timing Requirements

Administer RSVpreF vaccine only between 32 weeks 0 days and 36 weeks 6 days of gestation. 1

Seasonal Administration Algorithm:

• In most of the continental United States, vaccinate during September through January 1
• Start vaccination 1-2 months before anticipated RSV season onset 1, 2
• Continue through 2-3 months before anticipated season end 1
• For Alaska, southern Florida, Hawaii, Puerto Rico, Guam, U.S. Virgin Islands, and U.S.-affiliated Pacific Islands, follow local guidance due to different RSV seasonality 1

Minimum Protection Window:

• At least 14 days are required after maternal vaccination for adequate antibody development and transplacental transfer 7, 4
• Infants born <14 days after maternal vaccination may not receive adequate protection 7

Important Safety Caveats

Contraindications:

• History of severe allergic reaction (anaphylaxis) to any vaccine component 7
• Moderate or severe acute illness with or without fever (delay vaccination) 7

Special Populations:

• Infants born to immunocompromised mothers should receive nirsevimab regardless of maternal vaccination status 7
• Infants born at <34 weeks' gestation should receive nirsevimab even if mother was vaccinated 7

Co-Administration Safety

RSVpreF vaccine can be safely administered simultaneously with other recommended pregnancy vaccines including Tdap, influenza, and COVID-19 vaccines at different anatomic sites on the same day. 1, 4

Subsequent Pregnancies

Currently, no safety data exist for repeat RSV vaccination in subsequent pregnancies, and additional doses are not recommended until further data become available. 1, 8 The European Board and College of Obstetrics and Gynaecology specifically does not recommend repeat vaccination due to lack of data. 8

Common Pitfall to Avoid

Do not administer both maternal RSVpreF vaccine and infant nirsevimab for most infants—either strategy provides adequate protection, and both are not needed except for specific high-risk situations (preterm <34 weeks, immunocompromised mothers). 1, 2, 7