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The FDA’s approval of the maternal RSV vaccine marks a significant advancement in safeguarding young infants from the virus

With the approval of the first vaccine targeting respiratory syncytial virus (RSV) by the Food and Drug Administration on August 21, 2023, the United States is on the brink of acquiring a powerful new tool to shield infants from this highly contagious virus. RSV is a predominant cause of lower respiratory infections in young children, particularly severe for those under 6 months old. It stands as the primary reason for infant hospitalization in the U.S., contributing to approximately half a million ER visits, nearly 100,000 hospital admissions, and 300 fatalities among young children annually, as reported by the Centers for Disease Control and Prevention. The vaccine, marketed as Abrysvo, is sanctioned for administration between 32 and 36 weeks of pregnancy to offer protection to infants from birth through 6 months of age. The CDC is scheduled to convene in October to formulate recommendations for the use of Abrysvo, potentially making the vaccine accessible for pregnancy use in the coming months.

In mid-July, the FDA greenlit a long-acting, single-dose monoclonal antibody known as nirsevimab, marketed as Beyfortus, designed for infants and young children up to 2 years old as a preventive measure against respiratory syncytial virus (RSV). As an infectious disease epidemiologist and pediatric infectious disease physician, we have encountered the challenges posed by the limited preventive options for RSV, especially during the unusually severe RSV season in late 2022. The approval of both a maternal vaccine and a monoclonal antibody represents a significant advancement in the medical community’s capability to thwart RSV-related illnesses in children.

With these imminent options, parents of young children and expectant individuals may be contemplating the merits and drawbacks of each and deciding which is optimal for safeguarding their child from RSV.

A game-changing development in the battle against RSV, the newly sanctioned protein-based vaccine operates similarly to the Tdap (whooping cough) vaccine, administered between 27 and 36 weeks of pregnancy to shield babies against tetanus, diphtheria, and pertussis. Abrysvo prompts the mother’s immune system to generate antibodies that traverse the placenta, providing protection to the newborn against RSV starting at birth.

The FDA’s approval rested on clinical trial data from over 7,000 participants across 18 countries who received the RSV vaccine between 24 and 36 weeks of pregnancy or a placebo shot. In the trial, the maternal RSV vaccine exhibited efficacy, preventing 82% of severe lower respiratory illnesses caused by RSV in infants during the first 3 months of life and 69.4% through 6 months of age.

While the trial did not raise concerns about vaccine-related safety issues, including preterm birth, low birth weight, birth defects, developmental delays, or fatalities, the vaccine will carry a warning about a less-than-1% increase in preterm birth observed in the RSV vaccination group during the clinical trial. There is currently no evidence establishing a causal link between the vaccine and preterm birth, and the 1% increase was deemed statistically insignificant.

Furthermore, the FDA mandates ongoing safety monitoring by the vaccine manufacturer for pregnancy use. Notably, Abrysvo secured FDA approval in May 2023 for preventing RSV illness in adults aged 60 years and older.

Monoclonal antibodies offer an alternative protective measure for those unable to receive the RSV vaccine during pregnancy, providing pre-made antibodies to safeguard the baby.

Nirsevimab, or Beyfortus, is a monoclonal antibody endorsed for infants up to 8 months old during the RSV season and high-risk children up to 24 months old. Administered as a single shot, Beyfortus consists of laboratory-engineered human antibodies that defend against RSV-induced lower respiratory tract diseases, including bronchiolitis and pneumonia.

Clinical trial findings from 350 sites across 31 countries revealed Beyfortus’s 75% efficacy against RSV-associated lower respiratory illness and 62% effectiveness against RSV-associated hospitalization in the first 5 months post-birth. Mild adverse reactions included rashes and localized swelling or pain at the injection site. Children with a history of severe reactions to Beyfortus ingredients or bleeding disorders should either avoid or exercise caution when receiving it.

Comparatively, both the maternal vaccine and monoclonal antibody exhibited effectiveness in reducing severe RSV disease risk in infants, with similar efficacy and duration of protection observed in clinical trials. Abrysvo demonstrated protective effects up to 6 months of age, while Beyfortus provided protection up to 5 months of age.

While Abrysvo prompts the mother’s antibody production passed on to the baby, Beyfortus, not being a vaccine, delivers pre-made antibodies via injection. Beyfortus acts immediately post-administration, ensuring protection for babies born to vaccinated mothers. In contrast, Abrysvo requires approximately 14 days to generate effective antibodies in the mother after administration. The vaccine should be taken at least 14 days before the anticipated delivery date, ideally even earlier, to adequately shield the baby.

Both the vaccine and monoclonal antibody target the F-protein of the virus, crucial for viral cell entry and infection spread. Abrysvo induces antibodies against all F-protein sites, while Beyfortus targets a specific site, termed “site zero.” Both confer passive immunity, safeguarding babies during their most vulnerable period for severe RSV disease.

For infants born to mothers vaccinated within the specified window, Abrysvo suffices for protection. In cases where the mother isn’t vaccinated during pregnancy, Beyfortus is available for immediate administration post-birth.

Another significant distinction between the two products lies in their cost. Ready-made antibodies, like Beyfortus, can be expensive to manufacture, with a higher price tag compared to the Abrysvo vaccine – approximately $395 to $500 per Beyfortus shot versus $180 to $295 per Abrysvo shot. The cost and insurance coverage of Abrysvo will hinge on the CDC’s recommendations in October. However, both shots necessitate administration by a healthcare professional, requiring a medical visit.

While both options present a significant opportunity to prevent severe RSV-associated illness in newborns and young infants, the majority of children will not require both.

In certain circumstances, Beyfortus may be considered for infants born to mothers who received the vaccine. This could be suitable, for instance, if birth occurs within 14 days of vaccine administration or if the baby is premature. Additionally, the monoclonal antibody may be administered to safeguard high-risk infants, such as those with immune deficiency, chronic lung, or heart disease, up to their second year of life.

In summary, both offerings are deemed safe and efficacious, emphasizing the critical need to safeguard young infants and at-risk children from RSV.

Historically, viable monoclonal antibodies were primarily accessible for extremely premature infants. However, a considerable portion of infants affected by RSV are born at full term.

It is advisable for families to engage in conversations with their pregnancy care provider and pediatrician to explore the available options for RSV prevention.



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