Pfizer's RSV vaccine wins support of FDA panel despite lingering safety and efficacy questions

Though safety signals and study design vexed FDA expert advisers, Pfizer’s vaccine candidate for respiratory syncytial virus (RSV), Abrysvo, ultimately won over the group at a Tuesday meeting.

The question of the day? Whether the safety and efficacy of the shot—known in the clinic as RSVPreF—merits an approval to prevent lower respiratory tract disease caused by RSV in older adults.

On the first voting question around the safety of Pfizer’s Abrysvo in older adults, seven members of the FDA’s Vaccines and Related Biological Products Advisory Committee voted in favor of the shot, while four members voted against Abrysvo and one abstained.

Much of the concern centered on two cases of Guillain-Barré syndrome that cropped up in Pfizer’s clinical trials. FDA advisers had earlier flagged the rare risk.

Still, the majority of the FDA panel conceded that, based on the data currently available, Pfizer’s Abrysvo safety package looks sound.

On the second voting question—whether the available data support the effectiveness of Abrysvo for the prevention of lower respiratory tract disease caused by RSV in individuals 60 years of age and older—the results were the same: Seven panelists voted in favor of the vaccine, while four voted no and one abstained.

While most panel members suggested the data can support an approval, one expert, Henry Bernstein, D.O., argued there was just a “modest” amount of data in the patient groups most at risk from RSV. The doctors on the panel largely railed against issues with Pfizer’s study population, which included few older patients or those with underlying conditions and omitted immunocompromised patients.

The data, as presented, were “adequate for this general population, which isn’t the ideal population,” conceded another panelist, Stanley Perlman, M.D.

Despite those lingering concerns, the advisory committee win bodes well for Pfizer, which is locked in a heated race with GSK’s rival RSV vaccine candidate. GSK’s shot—destined to inherit the commercial moniker Arexvy—will itself go before the FDA’s vaccines and biologics committee Wednesday.

"We are encouraged by the outcome of today’s VRBPAC meeting as it is a testament to the strength of our science and dedication to bringing this important vaccine candidate to the market," Annaliesa Anderson, Ph.D., Pfizer's senior vice president and chief scientific officer for vaccine research and development, said in a statement. 

The FDA granted priority review to Pfizer’s Abrysvo application back in December.

In a pivotal phase 3 study, Pfizer’s shot was 66.7% effective at preventing an initial RSV episode in patients with two or more symptoms during the first RSV season. The vaccine was 85.7% effective at staving off RSV in patients with three or more symptoms.

Pfizer contends there’s a high unmet need for an RSV vaccine in both kids and adults. No RSV shot has ever been approved by the FDA, despite more than 50 years of development efforts. In infants, RSV is the leading cause of bronchiolitis and viral pneumonia and can lead to fatal respiratory distress in babies with underlying cardiopulmonary disease, according to Pfizer.

In older adults, for which Pfizer is angling for its first RSV approval, the company projects that the virus is responsible for between 60,000 and 160,000 hospitalizations each year. Over that same stretch, the virus causes between 6,000 and 13,000 deaths among patients ages 65 and up, the company says. Pfizer is specifically seeking an approval in adults 60 years of age and older.

Aside from the use in older adults, Pfizer is hoping to gain an approval for the shot as a maternal immunization to protect babies. That effort just picked up an FDA priority review and is set for an August decision.