GSK plc (LSE:GSK) announced Friday that the US Food and Drug Administration has expanded the approved age indication of Arexvy to adults aged 18 to 49 years at increased risk for lower respiratory tract disease caused by respiratory syncytial virus.

The vaccine was previously approved in the US for adults aged 60 and older, and adults aged 50 to 59 at increased risk for lower respiratory tract disease caused by RSV.

In the US, an estimated 21 million adults under 50 have at least one risk factor for severe RSV infection, according to data from the National Health and Nutrition Examination Survey.

The figure is based on 17% of adults aged 20 to 49 who had at least one risk factor, including congestive heart failure, coronary heart disease, stroke, chronic obstructive pulmonary disease, asthma, diabetes, liver disease, or renal disease.

The annual RSV burden among US adults aged 18 to 49 years includes about 17,000 hospitalisations, 277,000 emergency department admissions, and 1.97 million outpatient visits, based on a systematic review and meta-analysis of studies published between 2007 and 2021.

Most hospitalisations in younger adults occur in those with chronic medical conditions which place them at increased risk for severe RSV disease.

The FDA’s decision was supported by data from a Phase IIIb trial demonstrating a non-inferior immune response compared to adults aged 60 years and above.

The safety profile was consistent with findings from the broader Phase III programme that supported the initial US approval, with the most common adverse events being injection site pain, fatigue, myalgia, headache, and arthralgia within four days of vaccination.

The Phase IIIb trial enrolled 1,458 participants across 52 locations in six countries, including 16 US sites.

The study assessed the immune response in participants aged 18 to 49 with pre-defined stable chronic diseases leading to an increased risk for RSV disease, compared to those aged 60 years and above.