Dive Brief:

• Pfizer on Tuesday said it plans to ask regulators to broaden the approval of its vaccine for respiratory syncytial virus, or RSV, after the shot met the goal of a late-stage study testing it in adults as young as 18 years old.
• Pfizer’s vaccine, called Abrysvo and currently approved to prevent RSV-related disease in adults 60 years and older, spurred immune responses among people 18 to 59 years old that were equivalent to the data that secured its clearance in older adults, the company said. No RSV vaccine is approved for this age group.
• GSK, which sells a rival RSV vaccine to Abrysvo, has already asked the Food and Drug Administration for an expanded approval of its shot in adults between the ages of 50 and 59. A decision is expected in June.

Dive Insight:

GSK and Pfizer won the first and second approvals, respectively, of a vaccine for RSV, which causes tens of thousands of hospitalizations among older adults each year in the U.S. Pfizer subsequently secured clearance of maternal use of its vaccine, to confer temporary protection against RSV to newborns.

But, so far, GSK’s vaccine Arexvy has dominated the market, outselling Pfizer’s. Both drugmakers are looking to expand use of their shots to younger adults who are at higher risk of RSV disease, such as people who are immunocompromised.

The main part of Pfizer’s Phase 3 trial, dubbed Monet, enrolled 681 adults between 18 to 59 years old with conditions like chronic obstructive pulmonary disease, asthma and diabetes. A second part involved 200 participants who are immunocompromised, about half of whom were over the age of 60.

Pfizer said immune responses among those aged 18 to 58 were “non-inferior” to what it reported in another study called Renoir that enrolled more than 34,000 adults 60 years and older.

Infants, elderly and immunocompromised people are at higher risk of contracting severe disease from the virus. Severe RSV can cause worsening symptoms of chronic conditions such as asthma and chronic obstructive pulmonary disease.

While Pfizer said the shot was well-tolerated in its latest trial, regulators have previously scrutinized its association in very rare cases with a neurological condition called Guillain-Barré syndrome. Testing of both Abrysvo and Arexvy turned up a few cases of the syndrome, which advisers to the Centers for Disease Control and Prevention discussed at a recent meeting. The advisers judged the benefits of vaccination outweighed any risk in older adults, but that balance might be different in younger individuals.

Pfizer said it plans to publish full data from the study in a scientific journal and present them at a medical meeting.