What is the recommended RSV (Respiratory Syncytial Virus) prophylaxis for pregnant women?

RSV Vaccination for Pregnant Women

Pregnant women should receive the Pfizer RSVpreF vaccine at 32-36 weeks' gestation during September through January in most of the continental United States to protect their infants from severe RSV disease. 1

Recommended Vaccination Window

• Administer RSVpreF vaccine between 32 weeks 0 days and 36 weeks 6 days of gestation to optimize infant protection while minimizing potential preterm birth risk 2, 3
• The vaccine requires at least 14 days after administration for adequate maternal antibody development and transplacental transfer to protect the infant 4, 2
• Infants born less than 14 days after maternal vaccination should receive nirsevimab regardless of maternal vaccination status 2

Seasonal Timing

• Vaccinate during September-January in most of the continental United States, starting 1-2 months before anticipated RSV season onset 1, 4
• This timing ensures infants are in their first months of life (when most vulnerable) during peak RSV season 1
• For Alaska, southern Florida, Guam, Hawaii, Puerto Rico, U.S.-affiliated Pacific Islands, and U.S. Virgin Islands, follow local guidance due to different RSV seasonality patterns 1, 4

Safety Profile

The FDA approved this vaccine with specific gestational age restrictions based on safety data:

• In the approved 32-36 week dosing interval, preterm births occurred in 4.2% of vaccine recipients versus 3.7% of placebo recipients (not statistically significant) 3
• No statistically significant differences were observed for low birthweight or neonatal jaundice between vaccine and placebo groups 1
• The FDA determined benefits outweigh risks when administered at 32-36 weeks' gestation 3

Important caveat: The FDA labeled a warning for potential preterm birth risk because earlier trial data (24-36 weeks dosing) showed 5.7% preterm births in vaccine group versus 4.7% in placebo group, though not statistically significant 3. This is why the approved window is restricted to 32-36 weeks.

Simultaneous Administration

• RSVpreF can be administered simultaneously with Tdap, influenza, and COVID-19 vaccines at different anatomic sites on the same day 1, 4
• No need to space these vaccines apart 1

Alternative: Infant Nirsevimab

Either maternal RSVpreF vaccination OR infant nirsevimab is recommended, but both are not needed for most infants 1, 4:

• Discuss relative advantages of both options with patients and consider their preferences 1
• If the mother did not receive RSVpreF, the infant should receive nirsevimab if aged <8 months and born during or entering their first RSV season 4, 2

Exception requiring nirsevimab regardless of maternal vaccination:

• All infants born at <34 weeks' gestation should receive nirsevimab even if the mother was vaccinated 4, 2, 3

Duration of Protection

• Maternal vaccination provides protection that likely wanes after approximately 3 months, similar to maternal influenza and COVID-19 vaccines 1, 4, 2
• This waning is acceptable because seasonal timing ensures protection during the infant's most vulnerable first months during RSV season 1

Subsequent Pregnancies

• Current recommendation is for a single lifetime dose 1, 4
• No data currently exist on efficacy or safety of additional doses during subsequent pregnancies 1, 2
• ACIP may update recommendations as data become available 1

Common Pitfalls to Avoid

• Do not vaccinate before 32 weeks' gestation due to increased preterm birth signal in earlier gestational ages 3
• Do not vaccinate after 36 weeks 6 days' gestation as this is outside the approved window 2
• Do not vaccinate outside September-January in most of the continental US, as this reduces cost-effectiveness and may not provide protection during RSV season 1
• Do not assume both maternal vaccine and infant nirsevimab are needed for term infants—this is redundant for most 1, 4