Interim data find vaccine 66% to 85% effective against symptomatic RSV in older adults
The results from a large ongoing phase 3 trial show success in protection from respiratory syncytial virus (RSV)-associated lower respiratory tract illness on two important primary endpoints, although reductions in hospitalization and death have yet to be shown.
An investigational vaccine for respiratory syncytial virus (RSV) was effective against lower respiratory tract illness with multiple symptoms in older adults, according to an interim analysis of an industry-funded trial.
The results came from an ongoing, phase 3 trial of a bivalent RSV prefusion F protein-based vaccine. Researchers randomized adults ages 60 years and older to receive either a single intramuscular injection of the vaccine at a dose of 120 μg or placebo. Pfizer conducted the study, and results were published April 5 by the New England Journal of Medicine.
As of the interim analysis, 17,215 participants had received the vaccine and 17,069 had received the placebo. RSV-associated lower respiratory tract illness with at least two signs or symptoms occurred in 11 of the former group (1.19 cases per 1,000 person-years) and 33 of the latter (3.58 cases per 1,000 person-years), for a vaccine efficacy of 66.7% (96.66% CI, 28.8% to 85.8%). Illness with three signs or symptoms occurred in two (0.22 per 1,000 person-years) and 14 patients (1.52 per 1,000 person-years of observation) in each group, respectively, for an efficacy of 85.7% (96.66% CI, 32.0% to 98.7%). The trial did not have enough cases of severe lower respiratory tract illness (defined as hospitalization and illness warranting the use of oxygenation or mechanical ventilation) to evaluate that outcome. The incidence of local reactions was higher with the vaccine (12%) than with placebo (7%), but severe or life-threatening adverse events occurred in 0.5% and 0.4% of the respective groups. One case each of Guillain-Barré and Miller-Fisher syndromes occurred in vaccinated participants.
The study authors concluded that “the success criterion for vaccine efficacy was met with respect to RSV-associated lower respiratory tract illness with at least two signs or symptoms and at least three signs or symptoms (the two primary end points) and RSV-associated acute respiratory illness.” An accompanying editorial noted that a reduction in risk of hospitalization and death would be the most important effect of an RSV vaccine, and that has yet to be shown.
In February, an FDA advisory committee reviewed data on the vaccine and voted 7 to 4 in favor of its safety and effectiveness in adults 60 years and older. The FDA is expected to decide on approval of this vaccine and another developed by GSK by May, according to Reuters.