The FDA approved Pfizer’s bivalent respiratory syncytial virus (RSV) prefusion F protein vaccine (Abrysvo) for use in pregnant individuals to protect newborns from serious RSV-related outcomes.
Even though the vaccine was administered in trials starting at 24 weeks’ gestation, the agency approved giving the shot at 32 to 36 weeks’ gestation over a possible risk for preterm birth.
The vaccine is indicated for reducing the risk of RSV-related lower respiratory tract disease (LRTD) and severe LRTD in infants through 6 months of age.
In the phase III MATISSE study of about 7,000 pregnant patients, the vaccine showed an efficacy of 81.8% against severe LRTD in infants within 90 days after birth, and 69.4% within 180 days after birth, compared with placebo.
In a subgroup of about 3,000 pregnant people who got the shot at 32 to 36 weeks’ gestational age, the vaccine reduced infants’ risk of any medically attended LRTD by 34.7% within 90 days and 57.3% within 180 days. Risk for severe LRTD was reduced by 91.1% and 76.5%, respectively.
The numerical imbalance in preterm births in patients who received the vaccine — 5.7% versus 4.7% for those who got placebo — made it into the vaccine’s prescribing information, which includes a “warning to inform” about the difference.
The warning also “informs healthcare providers to avoid the potential risk of preterm birth” by giving the vaccine within the recommended window of 32 to 36 weeks, according to the FDA. Clinical studies of the vaccine excluded those at greater risk for preterm birth.