The FDA has approved an expanded indication for mRESVIA (mRNA-1345), Moderna’s respiratory syncytial virus (RSV) vaccine. The vaccine is now authorized for use in adults aged 18–59 years with an increased risk of RSV-related lower respiratory tract disease (LRTD). Approval was based on data from a Phase III trial, which demonstrated that mRESVIA met immunobridging criteria for both RSV-A and RSV-B strains, showing immune responses in high-risk younger adults comparable to those in the older adult population from a previous pivotal efficacy trial.¹

What Does the Expanded Approval of mRESVIA Mean for Younger Adults at Risk for RSV?

"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," said Stéphane Bancel, CEO, Moderna, in a press release.

Phase III Trial Details and Results

• The Phase III trial evaluated the safety and immunogenicity of mRESVIA in 1,150 adults aged 18-59 years with underlying health conditions.
• The trial was divided into two parts. Part A evaluated the safety and immune response of the vaccine, while Part B evaluated the safety and immune response in adults who received solid organ transplants.
• The dual primary endpoints of the trial were to demonstrate noninferiority of day 29 RSV-A and RSV-B neutralizing antibody (nAb) geometric mean titers (GMTs) for the 50-μg dose compared to those observed in adults aged ≥60 years from the Phase III pivotal efficacy trial.^1-3
• Results show that on day 29, mRESVIA met noninferiority criteria, with GMTs of 1.2 for RSV-A and 1.1 for RSV-B, and seroresponse rate differences of 11.8% for RSV-A and 10.8% for RSV-B, all within pre-specified confidence intervals.
• The vaccine was generally well tolerated. The most common adverse events included injection site pain, fatigue, headache, myalgia and arthralgia.^1,3

Regulatory Background and Designations

mRESVIA was first approved in May 2024 for the prevention of LRTD caused by RSV in people aged 60 years and older. In 2023, the vaccine was granted Breakthrough Therapy designation and in 2021, it was granted Fast Track designation.^4,5

Context Within the Broader RSV Landscape

mRESVIA marks the second RSV treatment this week to receive FDA approval. On Monday, Merck announced that the FDA approved Enflonsia (clesrovimab-cfor), a long-acting monoclonal antibody for the prevention of RSV in infants born during or entering their first RSV season.⁶

In April, the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices (ACIP) also voted to broaden its recommendation for RSV vaccines such as Pfizer’s Abrysvo to include adults aged 50 to 59 years with an increased risk for severe RSV-associated lower respiratory tract disease.⁷

According to the World Health Organization, RSV results in over 3.6 million hospitalizations and 100,000 deaths in children under five years of age annually. Around 97% of pediatric deaths from RSV occur in low- and middle-income countries where there is limited access to supportive medical care.

While the global estimates of adult RSV are unknown, it is estimated that in the United States, RSV results in up to 160,000 hospitalizations and 10,000 deaths in adults aged 65 years or older. This rate is higher in adults with underlying health conditions such as asthma, chronic obstructive pulmonary disease, or congestive heart failure.⁸

"We appreciate the FDA's review and thank all the participants in our clinical trial as well as the Moderna team for their dedication to protecting people against RSV,” continued Bancel, in the press release.

References

1. Moderna Receives U.S. FDA Approval for RSV Vaccine, mRESVIA, in Adults Aged 18–59 at Increased Risk for RSV Disease. Moderna. June 12, 2025. Accessed June 13, 2025. https://investors.modernatx.com/news/news-details/2025/Moderna-Receives-U-S--FDA-Approval-for-RSV-Vaccine-mRESVIA-in-Adults-Aged-1859-at-Increased-Risk-for-RSV-Disease/default.aspx

2. A Study to Investigate the Immunogenicity and Safety of mRNA-1345 Vaccine Targeting Respiratory Syncytial Virus (RSV) in High-risk Adults. Clinicaltrials.gov. Accessed June 13, 2025. https://clinicaltrials.gov/study/NCT06067230

3. Safety, Tolerability, and Immunogenicity of mRNA-1345 in Adults at Increased Risk for RSV Disease Aged 18 to 59 Years. Oxford Academic. Accessed June 13, 2025. https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaf292/8156665?login=false#google_vignette

4. FDA Approves mRESVIA (respiratory syncytial virus vaccine) for Prevention of Lower Respiratory Tract Disease Caused by RSV. Drugs.com. Accessed June 13, 2025. https://www.drugs.com/newdrugs/fda-approves-mresvia-respiratory-syncytial-virus-vaccine-prevention-lower-respiratory-tract-caused-6279.html

5. Moderna Granted FDA Breakthrough Therapy Designation for mRNA-1345, An Investigational Respiratory Syncytial Virus (RSV) Vaccine Candidate. Drugs.com. Accessed June 13, 2025. https://www.drugs.com/clinical_trials/moderna-granted-fda-breakthrough-therapy-designation-mrna-1345-investigational-respiratory-20653.html

5. Moderna Receives FDA Fast Track Designation for Respiratory Syncytial Virus (RSV) Vaccine (mRNA-1345). Drugs.com. Accessed June 13, 2025. https://www.drugs.com/clinical_trials/moderna-receives-fda-fast-track-designation-respiratory-syncytial-virus-rsv-vaccine-mrna-1345-19538.html

7. FDA Approves Merck’s Enflonsia to Prevent Respiratory Syncytial Virus. PharmExec. June 10, 2025. Accessed June 13, 2025. https://www.pharmexec.com/view/fda-approves-merck-enflonsia-prevent-respiratory-syncytial-virus

8. Pfizer, GSK Gain ACIP Recommendations for RSV and Meningococcal Vaccines. PharmExec. April 18, 2025. Accessed June 13, 2025. https://www.pharmexec.com/view/pfizer-gsk-gain-acip-recommendations-rsv-meningococcal-vaccines

9. Respiratory syncytial virus (RSV). WHO. Accessed June 13, 2025. https://www.who.int/news-room/fact-sheets/detail/respiratory-syncytial-virus-(rsv)