Why can't Respiratory Syncytial Virus (RSV) vaccine be administered after 36 weeks of gestation?

From the Guidelines

The RSV vaccine cannot be administered after 36 weeks of gestation because the FDA has approved it for use in pregnant persons at 32–36 weeks’ gestation to avoid the potential risk for preterm birth at <32 weeks’ gestation, which is associated with increased risk for morbidity and mortality 1.

Key Points

• The FDA has approved the RSVpreF vaccine for pregnant persons as a single dose during 32–36 completed gestational weeks to prevent RSV-associated lower respiratory tract disease in infants aged <6 months 1.
• The CDC’s Advisory Committee on Immunization Practices (ACIP) recommends RSVpreF vaccine for pregnant persons as a one-time dose during 32–36 weeks’ gestation using seasonal administration (September–January in most of the continental United States) to prevent RSV-associated LRTI in infants 1.
• Administration of the vaccine after 36 weeks of gestation may not provide sufficient protection against RSV-associated LRTI in infants, as the vaccine's efficacy is highest when administered during the recommended gestational age range 1.
• The potential risks associated with administering the vaccine after 36 weeks of gestation, including preterm birth and hypertensive disorders of pregnancy, outweigh the potential benefits 1.

Benefits and Risks

• The benefits of administering the RSVpreF vaccine during 32–36 weeks’ gestation include a 57.3% efficacy against medically attended RSV-associated LRTI in infants and a 76.5% efficacy against severe medically attended RSV-associated LRTI in infants 1.
• The risks associated with administering the vaccine during this time period include a potential increased risk of preterm birth and hypertensive disorders of pregnancy, although the differences were not statistically significant 1.

From the Research

RSV Vaccine Administration

The Respiratory Syncytial Virus (RSV) vaccine is not administered after 36 weeks of gestation due to several reasons:

• The vaccine is designed to be administered to pregnant women between 24-36 weeks of gestation to induce high levels of antibodies in the mother with high transplacental transfer to the fetus 2.
• Administering the vaccine after 36 weeks of gestation may not provide sufficient time for the transfer of antibodies to the fetus, reducing the efficacy of the vaccine 3.
• The vaccine has been shown to be effective in preventing severe RSV disease in infants when administered to pregnant women between 24-36 weeks of gestation, with an efficacy of 81.8% at 90 days and 69.4% at 180 days 2.

Vaccine Efficacy and Safety

The RSV vaccine has been shown to be effective and safe in preventing RSV-related lower respiratory tract disease in infants and older adults:

• The vaccine has been shown to have an efficacy of over 80% in the first 3 months of life to protect the infant from severe RSV-associated lower respiratory disease 4.
• The vaccine has also been shown to be effective in reducing the risk of RSV-related lower respiratory tract disease in older adults, with a vaccine efficacy of 78.3% 5.
• The rate of undesired side effects was low in all studies, and severe side effects were very rare 4, 5.

Recommendations

The RSV vaccine is recommended for use in pregnant women between 24-36 weeks of gestation to protect the newborn through the transplacental transfer of high-titer maternal antibodies:

• The vaccine is approved for use in pregnancy to protect the newborn, and has been shown to be safe and effective in clinical studies 3, 4.
• The American Academy of Pediatrics and other organizations recommend the use of the RSV vaccine in pregnant women between 24-36 weeks of gestation to protect the newborn against RSV disease 6.