GSK shares drop as US narrows recommendations for RSV vaccines

Shares in biopharma giant GSK tumbled on Thursday after a ruling by a US health agency narrowed usage recommendations for all respiratory syncytial virus (RSV) vaccines, restricting the addressable market for the company's Arexvy product.

Arexvy is currently approved by the Food and Drug Administration for the prevention of lung and lower airway infection caused by RSV in adults aged 60 and over.

However, the US Advisory Committee on Immunisation Practices (ACIP) of the Centers for Disease Control and Prevention said late on Wednesday that it was tightening its recommendations for adults in the 60-74 age category to those at risk of severe RSV, following feedback from the medical community. The ruling replaces the prior blanket "60+" years recommendation.

Meanwhile, a decision to extend the usage of RSV vaccines to those aged 50-59 was postponed pending more safety data.

According to analysts at Jefferies, the decision could cut the addressable US market in 2024-25 from around 80m 60-plus year-olds and 13m in the at-risk 50-59 category to just 55m people overall.

GSK's shares were down 5.1% at 1,518p by 1127 BST.