Moderna says its RSV shot is 50% effective after 18 months

Moderna Inc respiratory syncytial virus (RSV) shot mRESVIA showed 50% efficacy in preventing RSV after 18 months, the drugmaker said on Wednesday.

In their clinical trials, GSK’s RSV vaccine Arexvy was 78% effective in preventing severe RSV over a second year and Pfizer‘s was 78% effective through a second RSV season.

Moderna presented the data at a meeting of the U.S. Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices. The drugmaker has previously cautioned against comparing its vaccine to rivals, noting that the trials were not head-to-head and used different case definitions for RSV disease.

Shares of Moderna fell roughly 10% in trading Wednesday.