Vaccine Info

mRNA-1345 RSV Vaccine

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Last reviewed
January 30, 2023
Fact checked by
Robert Carlson, MD

mRNA-1345 Respiratory Syncytial Virus Vaccine 2023

Moderna Inc.'s mRNA-1345 Respiratory Syncytial Virus (RSV) vaccine candidate encodes for a prefusion F glycoprotein, eliciting a superior neutralizing antibody response. The mRNA-1345 vaccine is a messenger RNA (mRNA) vaccine. This mRNA is entirely made in a laboratory and instructs your body to make small pieces of proteins. In addition, this vaccine candidate contains the mRNA code for the RSV glycoprotein F, which does not cause RSV infection but helps the body's immune system recognize and protect itself if it encounters the virus. Therefore, you cannot become infected with RSV by receiving the investigational vaccine.

The Company shared the first interim analysis of the Phase 1 study of mRNA-1345, through 1-month post-vaccination, of the younger adult cohorts on April 14, 2021. Results showed the vaccine candidate generated a geometric mean rise in neutralizing antibodies relative to a baseline of at least 11-fold. Moderna's pivotal Phase, 3 placebo-controlled clinical study of mRNA-1345, evaluates its effectiveness in older adults (60 yrs+). As of January 30, 2023, the ConquerRSV study met its primary efficacy endpoints, including vaccine efficacy (VE) of 83.7% (95.88% CI: 66.1%, 92.2%; p<0.0001) against RSV-LRTD as defined by two or more symptoms and VE of 82.4% (96.36% CI: 34.8%, 95.3%; p=0.0078) in RSV-LRTD as defined by three or more symptoms.

The FDA had granted Fast Track and Breakthrough Designation designations for mRNA-1345 in adults older than 60. As of January 30, 2023, no U.S. Food and Drug Administration (FDA) approved RSV vaccines exist. 

Massachusetts-based Moderna's mRNA platform builds on continuous advances in basic and applied mRNA science, delivery technology, and manufacturing and has allowed the development of therapeutics and vaccines. To learn more, visit

mRNA-1345 Indication

The mRNA-1345 RSV vaccine candidate is indicated to prevent illness from RSV, a leading cause of respiratory illness in young children and older adults (65+). RSV is the most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia (infection of the lungs) in children younger than one year. According to the U.S. CDC, RSV leads each year, on average, to approximately 58,000 hospitalizations among children younger than five years old, 177,000 hospitalizations among adults 65 years and older, and 14,000 deaths among adults 65 years and older.

mRNA-1345 Dosage

The interim data from a Phase 1 study in older adults ages 65-79 showed that a single mRNA-1345 vaccination of 50 µg, 100 µg, or 200 µg boosted neutralizing antibody titers against RSV-A by approximately 14-fold and against RSV-B by about 10-fold. Data were pooled across dose levels because there was no significant difference between doses.

mRNA-1345 News For 2021 - 2023

January 30, 2023 - Stéphane Bancel, CEO of Moderna, stated: "With this designation, we look forward to productive conversations with the FDA in the hopes of bringing our RSV vaccine candidate for older adults to the market safely and quickly. Moderna's mRNA platform has now demonstrated two positive Phase 3 infectious disease trial results, and we continue to advance a portfolio of respiratory mRNA vaccines targeting the most serious diseases. We are grateful to the FDA for this designation."

January 17, 2023 - Stéphane Bancel, Moderna's CEO, stated: "Respiratory diseases are a major public health priority given they have a significant health impact and are a leading cause of hospitalization. For these reasons, in addition to our mRNA-1345 RSV vaccine candidate, we are committed to developing a portfolio of respiratory mRNA vaccines to target the most significant viruses causing respiratory disease, including COVID-19, influenza, and human metapneumovirus."

March 24, 2022 - Moderna confirmed a Phase 1 RSV trial (mRNA-1345) is ongoing evaluating tolerability, reactogenicity, and immunogenicity in children, younger adults, older adults, and women of childbearing age. In an interim analysis, mRNA-1345 boosted RSV-neutralizing antibodies and was well-tolerated at all doses in younger and older adults.

March 9, 2022 - ConquerRSV, a pivotal Phase 3 trial in adults ≥ 60 years of age; expected enrollment is ~34,000 participants in multiple countries.

February 24, 2022 - Moderna, Inc. reported full-year 2021 revenues of $18.5 billion.

February 22, 2022 - Stéphane Bancel, CEO of Moderna, stated in a press release, "Our ultimate goal is to combine our RSV vaccine with our COVID-19 and flu boosters into a single-dose booster."

November 18, 2021 - Moderna, Inc. announced the first participant had been dosed in the ConquerRSV Phase 2/3 study of mRNA-1345, the Company's Respiratory Syncytial Virus (RSV) vaccine candidate.

November 4, 2021 - Moderna announced a pivotal Phase 2/3 study of respiratory syncytial virus (RSV) vaccine candidate (mRNA-1345) in older adults expected to begin in 2021; the study is expected to enroll approximately 34,000 participants, subject to agreement with regulatory authorities.

August 3, 2021 - Moderna, Inc. announced that the U.S. FDA had granted Fast Track designation for mRNA-1345, its investigational single-dose mRNA vaccine against RSV in adults older than 60.

May 6, 2021 - Moderna Inc., investor presentation regarding mRNA-1345 vaccine candidate.

April 14, 2021 - Moderna shared the first interim analysis of the Phase 1 study after 1-month post-vaccination of younger adults (18-49). 'mRNA-1345 was shown to increase RSV neutralizing antibodies in seropositive younger adults. As expected, neutralizing antibodies were confirmed to be present at baseline in all participants. In addition, a single vaccination of mRNA-1345 at the 50 or 100 μg dose level boosted neutralizing antibody titers against both serotypes of RSV-A and RSV-B with no apparent dose response. At month 1, the geometric mean fold rise in neutralizing antibody relative to baseline was at least 20.5 for RSV-A and 11.7 for RSV-B.'

mRNA-1345 Clinical Trials

The pivotal ConquerRSV Phase 3 study of RSV in older adults (60+ years) is ongoingmRNA-1345 was generally well tolerated, with no clinically significant safety signals identified. To date, most solicited adverse reactions were mild or moderate, and the most commonly reported solicited adverse reactions in the mRNA-1345 group were injection site pain, fatigue, headache, myalgia, and arthralgia. The overall rate of severe (Grade 3 or greater) solicited systemic adverse reactions were 4.0% for mRNA-1345 and 2.8% for placebo.

Clinical Trial NCT04528719: A Dose Escalation Study to Evaluate Safety, Reactogenicity, and Immunogenicity of mRNA-1345 in Healthy Adults and Children Who Are Respiratory Syncytial Virus Seropositive. Estimated Completion Date: September 30, 2023. The study will be conducted in 2 phases: Phase 2 and Phase 3. In the Phase 2 segment, 400 and 2,000 participants will be randomly assigned to receive a single injection of either the mRNA-1345 vaccine at the selected dose or a placebo in a 1:1 randomization ratio.