On Jan. 17, 2023, Moderna announced positive topline data from its ConquerRSV Phase 3 pivotal efficacy trial of mRNA-1345, an investigational mRNA vaccine targeting respiratory syncytial virus (RSV) in older adults.

Following review by an independent Data and Safety Monitoring Board (DSMB), the primary efficacy endpoints had been met, including vaccine efficacy (VE) of 83.7% (95.88% CI: 66.1%, 92.2%; p<0.0001) against RSV-associated lower respiratory tract disease as defined by two or more symptoms.

The ConquerRSV trial was a randomized, double-blind, placebo-controlled study of approximately 37,000 adults 60 years or older in 22 countries, including the US. The primary efficacy endpoints were based on two definitions of RSV-LRTD defined as either two or more symptoms, or three or more symptoms of disease. The interim analysis was based on 64 cases of RSV-LRTD with two or more symptoms, of which 55 occurred in the placebo group and 9 occurred in the mRNA-1345 group, and 20 cases of RSV-LRTD with three or more symptoms, of which 17 cases were observed in the placebo group compared with three cases observed in the mRNA-1345 group.

The other primary efficacy endpoint against RSV-LRTD defined by three or more symptoms was also met, with a VE of 82.4% (96.36% CI: 34.8%, 95.3%; p=0.0078). The trial is ongoing, and additional efficacy analyses are planned as cases accrue, including for severe RSV.

RSV, a highly contagious seasonal respiratory virus and a leading cause of lower respiratory tract infections and pneumonia, causes a particularly large burden of disease in infants and older adults. RSV can cause severe disease with an estimated 5.2 million cases and nearly half a million hospitalizations in adults 60 years or older reported across high-income countries in 2019. Each year in the US, approximately 60,000-120,000 older adults are hospitalized, and 6,000-10,000 of them die due to RSV infection.