MFLUSIVA: A New mRNA Vaccine for Influenza (Flu)

In August 2026 the Food and Drug Administration (FDA) approved MFLUSIVA, an mRNA vaccine, to prevent influenza (flu).[1] The new vaccine is made with mRNA rather than viral components.[2] The Mflusiva vaccine should be available for the 2026-2027 influenza season.[3]

Mflusiva received full approval to prevent the 2026-2027 influenza strains in adults aged 50-64 years and accelerated approval based on immune responses for older adults.[4] Notably, several traditional influenza vaccines are approved for persons 6 months and older. A once-yearly Mflusiva dose is delivered with a single intramuscular injection.

mRNA vaccines work by introducing a piece of mRNA, which is the code for a viral surface protein, into the body. After cells in the body that are guided by the mRNA make the viral protein, the immune system recognizes the protein as foreign and produces antibodies that protect against infection. Traditional vaccines contain viral proteins that lead to antibody production.[5] Both types of influenza vaccine yield antibodies corresponding to the three viral strains approved by the FDA for the 2026-2027 influenza season.[6],[7]

FDA approval of Mflusiva was based on two randomized, activevaccine-controlled clinical trials.[8] The first trial compared the effectiveness of the trivalent 2024-2025 Mflusiva vaccine to the Fluarix Quadrivalent vaccine. More than 40,000 adults aged 50 years and older were randomized to receive one of these vaccines. The primary endpoint was genetically confirmed influenza with one or more symptoms, starting 14 days or later after vaccination. Median follow-up time was 181 days.

Participants in the Mflusiva group had significantly lower rates of influenza than those in the Fluarix group (2.0% versus 2.8%). The incidence of all three flu strains was lower in Mflusiva recipients, although the difference was not statistically significant for the rarest strain. A weakness of this study is that it did not use the CDCrecommended high-dose comparator vaccine for the subset of study participants who were 65 years of age and older.

The second trial involved participants 65 years of age and older and used a high dose of the Fluzone Quadrivalent vaccine as a comparator. The study was small (2,834 participants). The primary endpoint was immune responses 29 days after vaccination, not influenza cases. Although the second trial suggested that Mflusiva may be as effective or slightly more effective against influenza than the comparator vaccine in people 65 years of age and older, the FDA was not fully persuaded because the data were limited to the “surrogate outcome” of immune response. The FDA made continued approval of Mflusiva for this older age group contingent upon the completion of another trial to confirm its clinical benefit.[9]

The post-marketing randomized trial must be completed by 2030.[10] Other post-marketing studies will assess Mflusiva’s safety and effectiveness in children and adolescents.

For participants aged 50 to 65 years, the most common adverse reactions of Mflusiva were injection-site pain (69%), fatigue (48%), headache (42%), muscle (41%) or joint (32%) pain, chills (28%), and underarm swelling or tenderness (20%). People 65 years and older had similar adverse effects but at lower rates.

What You Can Do

Absent limited medical exceptions such as documented severe allergic reactions, Public Citizen’s Health Research Group recommends that all eligible children and adults receive and stay up to date on influenza vaccinations. For people 50 years of age and older, the new mRNA vaccine is an additional option. Any approved vaccine confers protection, approximately a 45% reduction in risk.

References

[1] Food and Drug Administration. BL 125869/0 approval and accelerated approval letter to ModernaTX. August 5, 2026. https://www.fda.gov/media/194121/download?attachment. Accessed September 2, 2026.

[2] Moderna US. Label: influenza vaccine (Mflusiva). August 2026. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=3dd1c6d2-b054-4803-bb21-460b1b090d4c&type=display. Accessed September 2, 2026. 

[3] Hashemi S. For the first time, an mRNA flu shot will be available to some people in the United States. Here’s what you should know. Smithsonian Magazine. August 11, 2026. https://www.smithsonianmag.com/smart-news/for-the-first-time-an-mrna-flu-shot-will-be-available-to-some-people-in-the-united-states-heres-what-you-should-know-180989305/. Accessed September 9, 2026.

[4] Moderna US. Label: influenza vaccine (Mflusiva). August 2026. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=3dd1c6d2-b054-4803-bb21-460b1b090d4c&type=display. Accessed September 1, 2026. 

[5] Centers for Disease Control and Prevention. How influenza (flu) vaccines are made. November 3, 2022. https://www.cdc.gov/flu/vaccine-process/index.html. Accessed September 2, 2026. 

[6] Moderna US. Label: influenza vaccine (Mflusiva). August 2026. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=3dd1c6d2-b054-4803-bb21-460b1b090d4c&type=display. Accessed September 1, 2026. 

[7] The 2026-2027 influenza (flu) and COVID-19 vaccines. Worst Pills, Best Pills News. September 2026. https://www.worstpills.org/newsletters/view/1746. Accessed September 2, 2026. 

[8] Moderna US. Label: influenza vaccine (Mflusiva). August 2026. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=3dd1c6d2-b054-4803-bb21-460b1b090d4c&type=display. Accessed September 1, 2026.

[9] Food and Drug Administration. BLA clinical review memorandum: 125869/0, Moderna, mRNA-1010. December 5, 2025. https://www.fda.gov/media/194140/download?attachment. Accessed September 3, 2026. 

[10] Food and Drug Administration. BL 125869/0 approval and accelerated approval letter to ModernaTX. August 5, 2026. https://www.fda.gov/media/194121/download?attachment. Accessed September 1, 2026.