Data unveiled on Thursday showed GSK’s GSK.L respiratory syncytial virus (RSV) vaccine was 82.6% effective in a keenly watched late-stage study involving older adults.

RSV is a leading cause of pneumonia in toddlers and the elderly, causing thousands of hospitalisations and deaths each year, but the complex molecular structure of the virus and safety concerns have stymied efforts to develop a vaccine.

The trial, which involved roughly 25,000 adults aged 60 and over, showed the vaccine was 94.1% effective against severe lower respiratory tract disease associated with an RSV infection, the British drugmaker said.

“These are truly exceptional results given that today RSV remains one of the major infectious diseases without a vaccine, despite over 60 years of research,” said Tony Wood, GSK Chief Scientific Officer, in a statement.

The company is a key player in the race to develop a safe and effective RSV vaccine, which, if approved, is expected to generate billions in sales for its maker. Regulatory submissions are planned for later this year.

If approved, Jefferies analysts have forecast $2.5 billion in global RSV vaccine peak sales in older adults for GSK.

GSK said in June the trial had yielded statistically significant results for the shot, but on Thursday gave details about the performance of the vaccine.

U.S. drugmaker Pfizer PFE.N in August disclosed positive Phase III data on its rival RSV vaccine in older adults.

Efficacy against RSV-associated lower respiratory tract illness with two or more symptoms was 66.7%, while efficacy against severe disease defined by three or more symptoms was 85.7%, the company said.

Given different definitions of the trial endpoints across the GSK and Pfizer studies, a direct comparison of efficacy is difficult, Morgan Stanley analysts said on Thursday.

“That said, the GSK data do look strong relative to that presented by Pfizer,” they added.

In trial participants with pre-existing conditions, the GSK vaccine was shown to be 94.6% effective, while in adults aged 70 to 79 it was 93.8% effective, the company said.

The performance of Pfizer’s vaccine across key subgroups, possible differences in safety and tolerability between the GSK and Pfizer shot, as well as any early signs of how durable the protection for either shot is, will be the key focus of presentations from both drugmakers at a medical conference next week, Jefferies analysts said.

A late-stage readout on Johnson & Johnson’s JNJ.N RSV vaccine in older adults is also expected by the end of 2022, while an interim look at Moderna’s MRNA.O rival shot’s Phase III data is also anticipated this winter.