On August 21, 2023, the FDA approved Abrysvo (Respiratory Syncytial Virus Vaccine; Pfizer), an intramuscular vaccine and the first vaccine for the active immunization of pregnant women at 32 to 36 weeks’ gestational age to prevent lower respiratory tract disease (LRTD) and severe LRTD resulting from respiratory syncytial virus (RSV) in newborns and infants up to age 6 months.
The FDA granted Abrysvo priority review and fast track and breakthrough therapy designations for this indication.
In May 2023, the FDA approved Abrysvo for the prevention of LRTD resulting from RSV in patients aged ≥60 years.
“RSV is a common cause of illness in children, and infants are among those at highest risk for severe disease, which can lead to hospitalization,” said Peter Marks, MD, PhD, Director of the FDA’s Center for Biologics Evaluation and Research, in a press release. “This approval provides an option for healthcare providers and pregnant individuals to protect infants from this potentially life-threatening disease,” he noted.
RSV is a very contagious virus that causes respiratory infections with cold-like symptoms in any age group and is the most common cause of lower respiratory tract infection in infants worldwide, which can lead to severe disease or death. RSV infection is especially common in young children and can lead to serious LRTD (eg, pneumonia, bronchiolitis). In infants and children, the risk for RSV-associated LRTD is highest during the first year of life.
In most areas of the United States, RSV infection is seasonal, typically starting in the fall and peaking in the winter. According to the Centers for Disease Control and Prevention, RSV is the leading cause of hospitalization in infants aged <1 year in the United States.
“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, MD, Clinical Professor, Pediatrics-Infectious Diseases, University of Colorado School of Medicine and Children’s Hospital Colorado, Aurora, in a press release. “The approval of…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,” he noted.
The FDA approved Abrysvo based on recent data from 2 international clinical trials. The pivotal study was the randomized, double-blind, multicenter, placebo-controlled, phase 3, clinical MATernal Immunization Study for Safety and Efficacy (MATISSE; NCT04424316; study 1), which was designed to evaluate the efficacy, safety, and immunogenicity of Abrysvo against LRTD and severe LRTD caused by RSV during pregnancy. Pregnant women who had an increased risk for preterm birth were excluded from the clinical studies of Abrysvo.
Study 1 included 3682 pregnant women who received Abrysvo and 3676 pregnant women who received a placebo. In a subgroup of pregnant women of 32 weeks’ through 36 weeks’ gestational age, approximately 1500 received Abrysvo and 1500 received placebo. Overall, Abrysvo reduced the risk for severe LRTD by 81.8% within 90 days after birth and by 69.4% within 180 days after birth. In the subgroup of pregnant women, Abrysvo reduced the risk for LRTD by 34.7% and the risk for severe LRTD by 91.1% within 90 days after birth compared with placebo. Within 180 days after birth, Abrysvo reduced the risk for LRTD by 57.3% and for severe LRTD by 76.5% compared with placebo. The median gestational age at birth was 39 weeks 1 day (range, 27 weeks 3 days-44 weeks 2 days).
Study 2 was a randomized, placebo-controlled, observer-blinded, phase 2 clinical trial (NCT04032093) that investigated the safety of 2 doses (120 mcg and a higher dose) of Abrysvo administered to pregnant women. Abrysvo 120 mcg was administered to 115 pregnant participants.
The most common (≥10%) side effects with Abrysvo in pregnant women were pain at the injection site (40.6%), headache (31.0%), muscle pain (26.5%), and nausea (20.0%). In addition, pre-eclampsia occurred in 1.8% of the women who received Abrysvo and in 1.4% of those who received placebo; gestational hypertension events were reported in 1.1% and 1%, respectively, of the patients. Furthermore, low birth weight was observed in 5.1% of the infants in the Abrysvo group and in 4.4% of the infants who received placebo. The rates of neonatal jaundice were 7.2% and 6.7%, respectively.
A numerical difference in preterm births was reported in Studies 1 and 2 among the patients who received Abrysvo compared with those who received placebo. In study 2, 6 of 114 (5.3%) births were preterm in the Abrysvo group and 3 of 116 (2.6%) births were preterm in the placebo group. In study 1, 202 of 3568 (5.7%) births were preterm in the Abrysvo group (95% confidence interval [CI], 4.9-6.5) versus 169 of 3558 (4.7%) births in the placebo group (95% CI, 4.1-5.5).
Therefore, the prescribing information for Abrysvo includes a warning about the risk for preterm births based on the numerical (but not significant) difference in preterm births in patients who received Abrysvo versus those who received placebo. The prescribing information indicates that these data are insufficient to establish or exclude a causal relationship between preterm birth and treatment with Abrysvo, but they reinforce the need to administer Abrysvo as indicated during 32 weeks to 36 weeks gestational age to avoid the risk for preterm birth.
Abrysvo is contraindicated in anyone with a history of severe allergic reaction (eg, anaphylaxis) to any of its components.
Abrysvo should be administered intramuscularly in a single (approximately 0.5 mL) dose and is provided in a kit that includes a vial of lyophilized antigen component, a prefilled syringe containing sterile water diluent component, and a vial adapter.
The FDA instructed the manufacturer to conduct postmarketing studies of Abrysvo to evaluate the risk for preterm birth, as well as the risk for hypertensive disorders of pregnancy, including pre-eclampsia.