(Reuters) - GSK's shares dropped more than 6% on Thursday, a day after a U.S. public health agency narrowed its usage recommendation for all respiratory syncytial virus (RSV) vaccines and held off on recommending their use for those under 60 years of age.

The U.S. Centers for Disease Control and Prevention (CDC) said late on Wednesday that it now recommended the shots for those who are 60-74 years old and have an increased risk of severe RSV due to medical conditions.

The decision is a negative for GSK, which makes the Arexvy RSV vaccine, analysts at JPMorgan wrote in a note.