Glaxo holds its breath

Though the separation of Glaxosmithkline's consumer care business Haleon is grabbing much of the attention, the group has another, strictly biotech, catalyst coming up. A pivotal trial of its respiratory syncytial virus (RSV) vaccine in the elderly is due to report by mid-year, and a great deal is riding on the results. 

The shot is Glaxo’s most valuable pipeline project, with some banks forecasting peak sales well into the billions despite the presence of jabs from Pfizer and Moderna in the late-stage pipeline. But Glaxo’s transition to pure-play biopharma raises the stakes: without the consumer care buffer, a negative readout could really hurt.

RSV is often thought of as a childhood disease, but in elderly people, especially those with asthma, heart disease or chronic obstructive pulmonary disease, the virus can be very severe and even fatal.

GSK3844766A is an adjuvanted vaccine containing a recombinant subunit pre-fusion RSV antigen (RSVPreF3). Its phase 3 efficacy study, Aresvi 006, has signed up 25,000 adults aged over 60.

Benchmarks

The trial’s primary endpoint is RSV with lower respiratory tract disease (RSV LRTD), which is a proxy for more severe infection. Analysts from Berenberg believe that efficacy of 90% or above would make ’766A “a clear winner”. Above 70% efficacy is likely to be viewed positively by the market, they add. 

Below that would be a disappointment. A vaccine with less than 70% efficacy might still be approvable, but might well be superseded by a superior competitor jab, Berenberg points out. And there are several vaccines from big pharma and others on which late-stage data in this same setting are imminent. 

Currently Glaxo is leading in terms of forecast sales, with $765m pencilled in for 2026 according to Evaluate Pharma’s sellside consensus. This has come down recently, however; at the end of last year 2026 forecasts sat at $1bn. This pre-dates the toxicity worries raised with Glaxo’s similar maternal RSV vaccine, GSK3888550A. Still, Berenberg puts peak sales of the adult vaccine at £3.7bn ($4.9bn).

Pfizer’s candidate takes second place, with 2026 forecasts of $444m; Leerink analysts forecast 2030 sales of $1.3bn here, so ’766A does not have a monopoly on blockbuster expectations. 

But success with an adult RSV vaccine is nowhere near as crucial for Pfizer as it is for Glaxo. For the UK company, the Aresvi 006 readout will be the first event by which investors judge New Glaxo’s R&D fortunes, and a miss will not be taken lightly.