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Considerations for RSV Vaccination During Pregnancy
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Key Takeaways
- RSV is a leading cause of newborn hospitalization, with severe cases causing bronchiolitis and pneumonia.
- Maternal RSV vaccination is recommended between 32 and 36 weeks of pregnancy to transfer protective antibodies to the newborn.
Respiratory syncytial virus (RSV) is the leading cause of newborn hospitalization in the US. Severe RSV may cause acute lower respiratory tract infection (LRTI), such as bronchiolitis and pneumonia. Between 2% and 3% of newborns younger than 6 months require hospitalization for RSV infection annually, and preterm newborns account for 25% of hospitalizations.1,2
Newborns are prone to infections | Image credit: Mediteraneo | stock.adobe.com
Newborns are prone to infections since their immune system is functionally immature and they have less effective immune responses to vaccinations. Therefore, the vaccination strategy is to provide protection to newborns and delay the first RSV infection until older, when they have a lower risk of severe RSV. A review article published in Nature Reviews Immunology discusses the current available and in-development vaccinations recommended during pregnancy and for newborns (defined as infants younger than 28 days old).2
The CDC recommends a single dose of the maternal RSV vaccine given September through January for patients between 32 and 36 weeks of pregnancy. If the patient is more than 36 weeks and 6 days pregnant, the CDC recommends a single dose of nirsevimab-alip (Beyfortus; Sanofi) be administered to the infant between October and March.3
Maternal RSV Vaccination
Maternal RSV vaccination provides protection to newborns because maternal antibodies cross the placenta and are secreted into breast milk. Immunoglobulin G (IgG) is the only antibody class that crosses the placenta, whereas mostly immunoglobulin A antibodies with low concentrations of IgG and immunoglobulin M transfers into breast milk. Based on the antibody transfer rate, vaccination later in pregnancy has been found to provide the most protection.2
The RSV prefusion (RSV pre-F) protein vaccine (Abrysvo; Pfizer) demonstrated efficacy of 81.8% against severe RSV-LRTI in infants younger than 3 months and 69.4% in those younger than 6 months. Although the phase 3 trial for RSV pre-F reported a non-statistically significant imbalance of preterm births, another RSV pre-F protein in development was halted in 2022 due to a significant difference in preterm births. Preterm birth rates are being closely monitored, and preterm newborns born before maternal vaccination may still benefit from breastfeeding.2
Because of the preterm birth risk, the RSV vaccine is indicated after 32 weeks of pregnancy and is contraindicated in pregnancies before 32 weeks and after 36 weeks during the beginning of the RSV season (September–January). Vaccination after 36 weeks does not provide enough time to develop antibodies, have them cross the placenta, and protect the newborn.2
Despite the benefits of maternal vaccination, uptake during pregnancy may be adversely affected by several factors, including lack of accessibility; hesitance due to safety concerns or misperception of disease risk; and distrust of vaccines, health care professionals, and health agencies.
RSV Vaccination After Birth
If vaccination is not possible or refused during pregnancy, a second strategy to protect newborns is vaccination after birth. The anti-RSV F protein monoclonal antibody nirsevimab-alip is novel in that it is long-acting with a half-life of 79 days. In a phase 3 trial, nirsevimab-alip demonstrated 74.5% efficacy against RSVI-LRTI up to 150 days in healthy term and preterm infants (>35 weeks of gestation) and efficacy of 70.1% in preterm infants (29 to <35 weeks of gestation). In a global clinical trial, the benefit of nirsevimab-alip was shown with efficacy of 83.2% against RSV-associated hospitalizations and 75.7% against RSV-associated very severe LRTI in infants younger than 12 months of age and born at a gestational age of at least 29 weeks.2
