Pfizer, jumping headfirst into the RSV vaccine race, kick-starts phase 3 test

Pfizer is starting a key late-stage trial of its experimental vaccine against a nasty form of a cold virus that can cause pneumonia and death in the young and old as the race to get a decent respiratory syncytial virus (RSV) vaccine on the market heats up.

The U.S. Big Pharma said the first subjects have now got their first shots of its RSV bivalent prefusion F subunit investigational vaccine candidate. This study is focused on patients over 60, who can suffer badly from RSV, while rival GlaxoSmithKline has recently started a maternal trial aimed at protecting pregnant mothers and their babies, another group that can be hit hard by the disease.

There is currently no vaccine available for the virus, which according to the CDC causes an average of 58,000 hospitalizations a year in the U.S., with 100-500 deaths among children younger than five years old as well as 177,000 hospitalizations with 14,000 deaths among adults aged 65 years or older.

Pfizer’s phase 3 clinical trial is set up to test the efficacy, immunogenicity, and safety of a single dose of its RSV vaccine, known as RSVpreF and will include around 30,000 older adults.

In early data dropped rather quietly during second-quarter earnings just over a month back, and to little fanfare, Pfizer said a challenge study, where vaccines were given to 62 adults under 50 who were then intentionally infected with RSV to see if the shot worked, showed “100% observed efficacy against mild to moderate symptomatic infection resulting from RSV.” 

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That was only a peek at the phase 2a test, which was set up to assess the immunogenicity and efficacy of the bivalent protein-based vaccine candidate, but was enough for Pfizer to say it would start a phase 3 in September, which it duly has.

It's not the only company in the space but has quickly pulled into the front of the race alongside GSK and J&J. GSK, however, faced a mixed bag in its development path. In July, it abandoned its RSV candidate in kids, while moving forward with that maternal vaccine study, with results expected in 2024. Pfizer is running a similar phase 3 in pregnant women. J&J, meanwhile, has an RSV vaccine, Ad26.RSV.preF, which is also in phase 3.

Pfizer’s RSV asset is set for 2026 sales of $255 million, according to EvaluatePharma, though the entire market could be $7 billion a year in adults alone, according to Leerink, so there is much up for grabs.

RSV, which hit historically low levels amid the pandemic last winter as people wore masks and observed social distancing, is starting to sweep back into view as countries unlock and remove masks.

Some epidemiologists are warning this could be a tough winter for all respiratory diseases with a mixture of delta-led COVID, RSV and influenza strains potentially hitting hard in the coming months. The elderly and young, with little recent immunity to RSV, are particularly vulnerable.

“RSV is a significant cause of severe respiratory disease in older adults, and it can cause disability and death. There is an important unmet medical need for an effective vaccine that can help protect older adults against this highly contagious disease,” said Kathrin U. Jansen, Ph.D., SVP and head of vaccine R&D at Pfizer Inc.

“The start of this phase 3 study is an important step forward towards our goal of comprehensive immunization against RSV disease, which includes developing a potential first vaccine to help prevent RSV disease in adults as well as the ongoing efforts to help protect infants through maternal immunization, subject to regulatory approval of the candidate vaccine.”