FDA Expands Moderna’s mRNA-1345 RSV Vaccine to Younger Adults
The federal agency approved the company’s mRNA-1345 (mRESVIA) vaccine for people who are between the ages of 18 to 59 years.
The FDA has expanded the approval of Moderna’s mRNA-1345 RSV vaccine to include people aged 18-59 years. This comes after last year’s initial approval of the vaccine for seniors 60 years of age and older in prevention of lower respiratory tract disease caused by RSV infection.1
"RSV poses a serious health risk to adults with certain chronic conditions, and today's approval marks an important step forward in our ability to protect additional populations from severe illness from RSV," Moderna CEO Stéphane Bancel, said in a statement. 1
This approval was supported by results from Moderna's phase 3 study, which evaluated the safety and immunogenicity of the vaccine in adults aged 18-59 with underlying health conditions. The immune responses against both RSV-A and RSV-B met prespecified non-inferiority immunobridging criteria when compared to those observed in adults aged 60 years and older in the pivotal phase 3, placebo-controlled safety and efficacy study. Comparable levels of neutralizing antibodies were observed across both the 18-49 and 50-59 age subgroups, supporting the vaccine's consistent immunogenicity profile in this at-risk, younger adult population.
These findings were presented at the U.S. Centers for Disease Control and Prevention's (CDC) Advisory Committee on Immunization Practices (ACIP) meeting in April 2025 and have been published in the journal, Clinical Infectious Diseases.1
Recent CDC ACIP Meeting
Back in April, the ACIP met and discussed Moderna’s vaccine with a focus on revaccination intervals and clinical/economic factors. The expansion of recommendations is under review, with a proposal to include at-risk adults aged 50–59 and potentially extend it to adults aged 18–49. The preliminary data from Moderna and GSK is not yet strong enough to warrant a vote. Vaccination trends show high uptake in year 1, followed by a decline in year 2 as recommendations narrow, with uncertain prospects for year 3.2
Previous Phase 3 Data
The phase 3 ConquerRSV trial was a randomized, double-blind, placebo-controlled study of approximately 37,000 adults who are 60 years or older across 22 countries. The investigators based their primary efficacy endpoints around 2 definitions of RSV-LRTD defined as either two or more symptoms, or three or more symptoms of disease.2
The interim analysis was based on 64 cases of RSV-LRTD with 2 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.3
A subsequent analysis from the ConquerRSV study with a longer median follow-up duration of 8.6 months (versus 3.7 months in the primary analysis), with a range of 15 days to 530 days, and including subjects from the Northern and Southern Hemispheres was recently presented at the RSVVW'24 conference. In this supplemental analysis, mRNA-1345 maintained durable efficacy, with sustained VE of 63.3% (95.88% CI: 48.7%, 73.7%) against RSV-LRTD including two or more symptoms. VE was 74.6% (95% CI: 50.7%, 86.9%) against RSV-LRTD with ≥2 symptoms, including shortness of breath and 63.0% (95% CI: 37.3%, 78.2%) against RSV-LRTD including three of more symptoms.4
