What is the optimal timing for administering Abrysvo (Respiratory Syncytial Virus vaccine) during pregnancy?

From the Guidelines

The optimal timing for administering Abrysvo (RSV vaccine) during pregnancy is between 32 and 36 weeks of gestation. This specific window is recommended because it allows sufficient time for maternal antibody production and transfer across the placenta to the fetus before birth, as supported by the Advisory Committee on Immunization Practices (ACIP) recommendations 1. A single dose of Abrysvo (0.5 mL) should be administered as an intramuscular injection, typically in the deltoid muscle. The vaccine should not be given before 32 weeks as earlier administration may result in waning antibody levels by the time of birth, potentially providing less protection to the newborn. Administration after 36 weeks risks insufficient time for optimal antibody development and transfer before delivery. This timing maximizes passive immunity for the infant during their first months of life when they are most vulnerable to severe RSV disease. The protection provided to infants through maternal vaccination is particularly important since RSV is a leading cause of hospitalization in infants under 12 months of age, with the highest risk occurring in the first 6 months of life.

Key points to consider:

• The ACIP recommends RSVpreF vaccine for pregnant persons as a one-time dose during 32–36 completed weeks’ gestation using seasonal administration (September–January in most of the continental United States) to prevent RSV-associated lower respiratory tract infection (LRTI) in infants aged <6 months 1.
• Either maternal RSVpreF vaccination during pregnancy or nirsevimab administration to the infant is recommended to prevent RSV-associated LRTI among infants, but both are not needed for most infants 1.
• The vaccine efficacy was calculated as (1 − [hP / (1 − P)]) x 100%, where P is the number of cases in the RSVpreF group divided by the total number of cases and h is the ratio of number of participants at risk in the placebo group to the number of participants at risk in the RSVpreF group 1.
• The most recent guidelines from 2023 support the use of Abrysvo during pregnancy at 32-36 weeks gestation, with the ACIP recommending its use for pregnant individuals at this time to protect infants under 6 months from RSV-associated lower respiratory tract infections 1.

Given the evidence, administering Abrysvo between 32 and 36 weeks of gestation is the recommended approach to balance the benefits of maternal vaccination against the potential risks, prioritizing the health outcomes of both the mother and the infant 1.

From the FDA Drug Label

ABRYSVO is a vaccine indicated for active immunization of pregnant individuals at 32 through 36 weeks gestational age for the prevention of lower respiratory tract disease (LRTD) and severe LRTD caused by respiratory syncytial virus (RSV) in infants from birth through 6 months of age. Potential risk of preterm birth. To avoid the potential risk of preterm birth with use of ABRYSVO before 32 weeks of gestation, administer ABRYSVO as indicated in pregnant individuals at 32 through 36 weeks gestational age.

The optimal timing for administering Abrysvo during pregnancy is between 32 and 36 weeks of gestational age.

• Evidence for administration: The vaccine is indicated for active immunization of pregnant individuals at 32 through 36 weeks gestational age for the prevention of lower respiratory tract disease (LRTD) and severe LRTD caused by RSV in infants from birth through 6 months of age 2.
• Evidence against administration before 32 weeks: There is a potential risk of preterm birth with use of Abrysvo before 32 weeks of gestation, therefore it is recommended to administer the vaccine as indicated in pregnant individuals at 32 through 36 weeks gestational age 2. There is no specific evidence to support administration at 36 weeks vs 32 weeks, the recommendation is to administer the vaccine between these two time points.

From the Research

Summary of Evidence for Abrysvo (Respiratory Syncytial Virus Vaccine) During Pregnancy

• There is no direct evidence provided for the use of Abrysvo during pregnancy.
• However, the provided studies discuss the use of palivizumab, a monoclonal antibody for preventing severe RSV infection in children, which may be relevant for understanding the potential effects of Abrysvo.

Evidence for Palivizumab

• A study published in 2021 3 found that palivizumab reduces hospitalization due to RSV infection, with high certainty evidence.
• The same study found that palivizumab probably results in little to no difference in mortality or adverse events, with moderate certainty evidence.
• A 1998 study 4 recommended palivizumab for infants who were 32 to 35 weeks of gestation at birth, and found that it provides benefit for these infants.
• A 2017 review 5 discussed the safety and efficacy of palivizumab in preventing RSV-associated hospitalizations in high-risk infants.
• A 2020 expert consensus 6 recommended palivizumab for preterm infants, former preterm children with chronic lung disease, and children with significant congenital heart disease.
• A 2023 review 7 found that palivizumab can lead to a reduction in RSV-related hospitalization in high-risk populations, but has not been demonstrated to reduce mortality, adverse events, or length of hospital stay related to RSV.

Optimal Timing for Administering Abrysvo

• There is no direct evidence provided for the optimal timing of administering Abrysvo during pregnancy.
• However, the studies on palivizumab suggest that the optimal timing for administering prophylaxis may depend on the individual's risk factors and the RSV season.
• The 2020 expert consensus 6 recommended administering up to 5 monthly doses of palivizumab over the RSV season.
• The 1998 study 4 suggested that palivizumab may be beneficial for infants who were 32 to 35 weeks of gestation at birth, which may inform the optimal timing for administering Abrysvo during pregnancy.