RSV Vaccine Abrysvo Approved for Use During Pregnancy to Protect Infants

The Food and Drug Administration (FDA) has approved Abrysvo^™ (respiratory syncytial virus vaccine) 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.

Abrysvo is an unadjuvanted bivalent vaccine containing recombinant RSV prefusion F (preF) A and RSV preF B. The approval was based on data from the randomized, double-blind, placebo-controlled phase 3 MATISSE trial (ClinicalTrials.gov Identifier: NCT04424316), which evaluated the efficacy of Abrysvo in preventing RSV-associated LRTD in infants born to individuals vaccinated during pregnancy.

Maternal participants were randomly assigned to receive either Abrysvo (n=3695) or placebo (n=3697). Vaccine efficacy, defined as the relative risk reduction of RSV-associated LRTD and severe RSV-LRTD in infants born to individuals who received Abrysvo vs those who received placebo, was evaluated within 90, 120, 150, and 180 days after birth.

Results showed vaccine efficacy of 81.8% (99.5% CI, 40.6-96.3) against severe LRTD caused by RSV in infants from birth through the first 90 days of life (6 cases in the vaccine group and 33 cases in the placebo group). Efficacy of 69.4% (97.58% CI, 44.3-84.1) was observed over the 6-month follow-up period (19 cases in the vaccine group and 62 cases in the placebo group).

While the second primary endpoint did not meet statistical significance, vaccine efficacy against RSV-associated LRTD was reported to be 57.1% (99.5% CI, 14.7-79.8) in infants from birth through the first 90 days of life and 51.3% (97.58% CI, 29.4-66.8) over the 6-month follow up period.

Among individuals who were 32 through 36 weeks gestational age, 1572 participants received Abrysvo and 1539 received placebo. Findings showed Abrysvo reduced the risk of severe LRTD by 91.1% (95% CI, 38.8-99.8) within 90 days after birth and by 76.5% (95% CI, 41.3-92.1) within 180 days after birth compared with placebo. Vaccine efficacy against LRTD was reported to be 34.7% (95% CI, -34.6, 69.3) within 90 days after birth and 57.3% (95% CI, 29.8-74.7) within 180 days after birth.

The most commonly reported solicited local and systemic adverse reactions in pregnant individuals (≥10%) were pain at the injection site (40.6%), headache (31%), muscle pain (26.5%), and nausea (20%). Serious adverse reactions reported at a higher rate with Abrysvo compared with placebo included preeclampsia (1.8% vs 1.4%) and gestational hypertension (1.1% vs 1.0%).

A numerical imbalance in preterm births was also observed in the MATISSE trial (5.7% in the Abrysvo group vs 4.7% in the placebo group), though data were insufficient to establish or exclude a causal relationship. The FDA is requiring Pfizer to conduct postmarketing studies to further assess the potential risks of preterm birth and hypertensive disorders.

Adverse events in infants were reported at similar frequency between the vaccine and placebo groups.

Abrysvo is supplied in a kit containing a vial of lyophilized antigen component, a prefilled syringe containing diluent and a vial adapter. The lyophilized antigen component should be reconstituted with the accompanying sterile water diluent component to form a single dose that is administered intramuscularly.

Abrysvo is also indicated for the prevention of LRTD caused by RSV in individuals 60 years of age and older.