Ask the Experts: Influenza

Moderna’s mFlusiva is the first FDA-approved mRNA influenza vaccine. FDA approved it on August 5, 2026, for people age 50 years and older. It is not approved for use during pregnancy due to a lack of data on its use during pregnancy. It is supplied as a preservative-free, single-dose prefilled syringe and is administered as a 0.38 mL intramuscular dose. It is contraindicated for people who have had a severe allergic reaction (e.g., anaphylaxis) to a prior dose of mFlusiva or to a component of the vaccine. It contains no egg protein, preservatives, or antibiotics; it does contain polyethylene glycol (PEG). It is stored at standard temperatures for refrigerated vaccines: 2° to 8°C (36° to 46°F); it should never be frozen. It may be kept at room temperature, at 8° to 25°C (46° to 77°F), for up to 12 hours, but it should not be returned to the refrigerator after room-temperature storage begins. FDA information, including the package insert, is available at www.fda.gov/vaccines-blood-biologics/vaccines/mflusiva.

A large-scale, randomized clinical trial comparing its effectiveness to a standard, egg-based inactivated influenza vaccine (IIV) found it to be moderately superior to standard egg-based IIV, preventing 26.6% more cases of influenza infection in the study population age 50 years and older. This result is similar to the 24.4% relative reduction in influenza infections measured in a randomized clinical trial comparing high-dose influenza vaccine (HD-IIV) to standard, egg-based IIV among adults age 65 years and older that was published in 2014. Side effects, including injection site pain, fatigue, headache, and other systemic symptoms were significantly more common in mFlusiva recipients, but were generally mild and lasted a median of two days. 

A separate study in people age 65 years and older measured a somewhat stronger antibody response to mFlusiva compared to HD-IIV; however, this serologic study did not compare the products’ relative effectiveness at preventing clinical infections.  Further studies of mFlusiva’s clinical effectiveness in people age 65 years and older are planned. 

The September 1, 2026, CDC interim clinical considerations for the use of 2026–27 influenza vaccines are silent on mFlusiva. The American Academy of Family Physicians (AAFP) recommends mFlusiva as one of four preferred options for adults age 65 years and older, based upon the clinical trial evidence of its superior effectiveness against influenza infection compared to standard IIV. View the AAFP 2026–27 season recommendations for COVID-19, influenza, and RSV vaccination of immunocompetent adults and healthcare personnel at www.aafp.org/assets/image/upload/v1788277985/pdf_2026_through_2027_influenza_rsv_sars_covid_2_guidance.pdf.