Investigational RSV Vaccine Demonstrates 83.7% Efficacy in Clinical Trial


Based on study findings, Moderna plans to submit for regulatory approval in the first half of 2023 for mRNA-1345, a novel vaccine for respiratory syncytial virus.

Moderna has announced encouraging results from a clinical trial of mRNA-1345, an investigational vaccine for respiratory syncytial virus (RSV).

The mRNA-1345 vaccine is an investigational RSV vaccine that consists of a single mRNA sequence encoding for a stabilized prefusion F glycoprotein. It uses the same lipid nanoparticles as the Moderna COVID-19 vaccines.

According to results from the ConquerRSV phase 3 pivotal efficacy trial, the vaccine demonstrated an efficacy of 83.7% against RSV lower respiratory tract disease, defined by 2 or more symptoms in older adults. Based on these findings, Moderna plans to submit for regulatory approval in the first half of 2023, according to a press release.

“Today’s results represent an important step forward in preventing lower respiratory disease due to RSV in adults 60 years of age and older,” said Stephane Bancel, chief executive officer of Moderna, in the press release. “These data are encouraging and represent the second demonstration of positive phase 3 trial results from our mRNA infectious disease vaccine platform after Spikevax, our COVID-19 vaccine. We look forward to publishing the full data set and sharing the results at an upcoming infectious disease medical conference.”

The ConquerRSV trial is a randomized, double-blind, placebo-controlled study of approximately 37,000 adults 60 years of age or older in 22 countries, including the United States. The primary efficacy endpoints were based on 2 definitions of RSV-associated lower respiratory tract disease (RSV-LRTD) defined as either 2 or more symptoms, or 3 or more symptoms of disease.

The interim analysis was based on 64 cases of RSV-LRTD with 2 or more symptoms. Of those cases, 55 occurred in the placebo group and 9 occurred in the mRNA-1345 group. Furthermore, 20 cases of RSV-LRTD with 3 or more symptoms were seen, of which 17 were observed in the placebo group compared with 3 in the mRNA-1345 group.

The other primary efficacy endpoint against RSV-LRTD defined by 3 or more symptoms was also met, with a vaccine efficacy of 82.4%. The trial is ongoing and additional efficacy analyses are planned as cases accrue, including for severe RSV.

A concurrent review of available safety data was also conducted, and the vaccine was well tolerated with no safety concerns identified. Safety and tolerability will continue to be followed. To date, most solicited adverse events (AEs) were mild or moderate. The most commonly reported solicited AEs in the mRNA-1345 vaccine group were injection site pain, fatigue, headache, myalgia, and arthralgia.

The overall rate of severe (grade 3 or higher) solicited systemic AEs was 4% for mRNA-1345 and 2.8% for placebo. The overall rate of grade 3 or greater solicited local AEs was 3.2% for mRNA-1345 and 1.7% for placebo.

“RSV significantly affects the health of older and high-risk adults, particularly those with comorbidities,” Abdullah Baqui, MBBS, a principal investigator for the study sites in Bangladesh, said in the press release. “This trial will help to understand the role of severe acute respiratory infections in older adult populations and inform the future implementation of vaccines in adults in lower-resource areas.”


Moderna Announces mRNA-1345, an Investigational Respiratory Syncytial Virus (RSV) Vaccine, Has Met Primary Efficacy Endpoints in Phase 3 Trial in Older Adults. News release. Moderna; January 17, 2023. Accessed January 19, 2023.

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