Pfizer Eyes Broader Label for RSV Vaccine Abrysvo After Promising Phase III Data

Pfizer_iStock, JHVEPhoto

Pictured: Signage at Pfizer's office in Canada/iStock, JHVEPhoto

Pfizer on Tuesday unveiled top-line data from its Phase III MONeT trial, showing that its respiratory syncytial virus vaccine Abrysvo could induce immune protection in adults 18 to 59 years of age.

Abrysvo hit MONeT’s co-primary immunogenicity endpoints, eliciting a non-inferior neutralizing response to the RSV-A and RSV-B virus subgroups, compared with the vaccine’s effect in elderly adults aged 60 and older, as demonstrated in the Phase III RENOIR study which established the safety and efficacy of the vaccine.

According to Tuesday’s results, vaccination with Abrysvo also elicited a fourfold increase in serum neutralizing titers against RSV-A and RSV-B one month after inoculation.

In terms of safety, MONeT found Abrysvo to be well-tolerated. The vaccine’s safety and adverse event profile was consistent with what had been established in previous studies.

Annaliesa Anderson, head of vaccine research and development at Pfizer, in a statement called these findings “encouraging,” adding that they provide strong evidence of Abrysvo’s protective effects in younger adults who are at higher risk of respiratory syncytial virus (RSV)-associated illnesses.

Pfizer will file these data with regulatory health agencies, proposing a broader label for Abrysvo. If approved, Abrysvo could become “the first and only RSV vaccine for adults 18 years and older,” Anderson said.

Abrysvo snagged the FDA’s approval in June 2023, one month behind its chief competitor Arexvy, which is being developed and commercialized by GSK. Both vaccines are indicated for the prevention of lower respiratory tract disease (LRTD) in adults 60 years of age and older.

In August 2023, Pfizer secured a label expansion for Abrysvo, allowing its use in pregnant women at 32 through 36 weeks of gestation, to prevent RSV-associated LRTD in their infants.

Despite having a broader label and a potentially larger target patient population, Abrysvo has lagged far behind Arexvy. In November 2023, CFO David Denton said in an investor event that the pharma is “disappointed” in Abrysvo’s performance.

GSK’s Arexvy at the time was well on its way to blockbuster status. The company in its third-quarter 2023 earnings report claimed that Arexvy had captured two-thirds of retail vaccinations in the U.S. and brought in nearly $860 million in its first full quarter on the market.

Like Pfizer, GSK is also working to expand Arexvy’s label, though it has so far focused on the adult population. In October 2023, GSK unveiled early results from a Phase III trial testing Arexvy in younger seniors—those 50 to 59 years of age. The British pharma did not reveal specific data but said that the vaccine was just as safe and effective in the younger age group as in its currently approved population.

Tristan Manalac is an independent science writer based in Metro Manila, Philippines. Reach out to him on LinkedIn or email him at or

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