Vaccine for Respiratory Syncytial Virus in Infants Granted Breakthrough Therapy Designation

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The immunization, meant to protect infants aged six months or lower, is given to pregnant individuals at a gestation period of 32 to 36 weeks.

On Aug. 21, 2023, Pfizer announced that FDA granted Breakthrough Therapy Designation for ABRYSVO, an immunization given to pregnant individuals at a gestation period of 32 to 36 weeks to prevent Respiratory Syncytial Virus (RSV) in infants. According to Pfizer, this is the first US approval of a maternal vaccine to protect infants from birth to six months from lower respiratory tract disease (LRTD) due to RSV. RSV affects around 500,000 to 600,000 infants each year, and nearly all children experience an RSV infection by the time they are two years old. This vaccine aims to protect infants ages six months or lower, who are most venerable to serious consequences from RSV.

The approval decision is based on data from the Phase III clinical trial, a randomized, double-blinded, placebo-controlled study which included over 7000 pregnant individuals. The results were published in The New England Journal of Medicine in April 2023. ABRYSVO is a bivalent RSV prefusion F vaccine; it is unadjuvanted and made of two preF proteins meant to enhance protection against RSV A and B strains. According to Pfizer, it is the only company with an RSV vaccine to protect older adults, as well as infants through maternal immunization.

There will be two additional clinical trials evaluating ABRYSCO. One will be in children ages 2–<18 with higher risk for RSV, while the other will evaluate immunocompromised adults ages 18 and older at high risk for RSV. Safety information for ABRYSCO can be found on Pfizer’s website.


“Newborns and young infants—whose immune systems are still developing and are not yet strong enough to defend against infections—may now be protected from RSV from the moment of birth through maternal immunization,” said Eric A.F. Simões, M.D., Clinical Professor, Pediatrics-Infectious Diseases, University of Colorado School of Medicine and Children’s Hospital Colorado, Aurora, in a Pfizer press release. “The approval of Pfizer’s ABRYSVO is a major triumph as it helps ensure no delay in potential RSV protection during an infant’s most vulnerable first six months of life and offers healthcare providers a new opportunity to help prevent severe RSV.”

Source: Pfizer