GSK vaccine R&D head touts consistency of RSV data but is mum on restarting maternal trial

GSK’s head of vaccine R&D, Phil Dormitzer, M.D., Ph.D., can almost taste regulatory success as the company soon approaches an FDA deadline for a decision on its respiratory syncytial virus (RSV) vaccine in older adults. If approved, it could become the first in the world. 

But Dormitzer wouldn’t commit to restarting maternal trials of the vaccine, which GSK closed down a year ago after a safety signal arose. His comments in an interview with Fierce Biotech come as the company is the first among the three Big Pharmas in the race for an adult RSV vaccine to publish full data from its phase 3 trial. 

The peer-reviewed article, published Wednesday night in The New England Journal of Medicine, highlights much of the top-line data disclosed by GSK in late 2022. But new details do provide a critical distinction between the British Big Pharma and its competitors. Namely, the vaccine performed well in patients with at least one comorbidity, with 94.6% efficacy in that population. 

The supplemental portion of the paper also explains that GSK defined severe disease as having two or more lower respiratory signs or as indicated by a primary investigator. Lower respiratory signs include, among others, wheezing, low or decreased oxygen levels and new or increased crackles. It’s an important clarification, with the company posting 94.1% efficacy among that population. The two other companies described efficacy in patients with three or more RSV-associated symptoms of lower respiratory tract disease, not signs. Pfizer said its vaccine was 85.7% effective in that population, while Moderna reported an 82.4% efficacy rate. 

“The thing that impresses me most is the consistency,” said Dormitzer, who jumped from Pfizer to GSK in December 2021. He underscored the vaccine's ability to prevent not just lower respiratory tract disease, but also acute respiratory illness, with GSK reporting a 71.7% efficacy against the latter. 

But while Dormitzer feels the company is in a “leading spot,” he wouldn’t commit to the company restarting trials testing the vaccine in pregnant women, saying only that he deferred to a presentation slated for ReSViNET’s annual conference at the end of the month. GSK halted its phase 3 trial in pregnant women a year ago after a safety signal arose.

Regulators are reviewing Sanofi’s antibody to protect against RSV in infants, while Pfizer and Moderna are working on maternal and pediatric vaccines, respectively. 

“I think at this point, I’d like to let the data speak for itself,” he said. “We will speak to the data, as well, but I think we just have a better discussion once the data are out.” Dormitzer also declined to comment on the potential cost of the vaccine, saying that wasn’t under his purview. 

Dormitzer’s confidence and GSK’s dataset come as the company nears a May 3 deadline for the FDA to decide on the company’s approval application. Pfizer similarly expects to hear from the FDA by May. 

Editor's note: This story was updated to correct GSK's definition of severe disease in the phase 3 trial. A spokesperson for the company said Dormitzer misspoke, referring Fierce Biotech to the peer-reviewed article's supplemental document.