Moderna began shipping doses of its mRNA-based flu vaccine mFlusiva across the United States. The distribution marks the arrival of the first flu vaccine in the country to use messenger RNA technology.

The Food and Drug Administration approved MFLUSIVA for use in persons 50 years of age and older. CVS Health said mFlusiva is available at its U.S. pharmacies following the start of shipments. Walgreens expects to begin receiving shipments of the vaccine any day now, although it will be available to patients in limited quantities this season.

The regulatory clearance followed a unanimous recommendation in June from the FDA’s independent vaccine advisory panel for older adults. The agency granted traditional approval for adults 50 to 64 and accelerated approval for people 65 and older. Moderna is required to conduct another clinical trial in the 65 and older age group as part of the approval conditions.

Evidence for the vaccine's efficacy came from a late-stage clinical trial published in the New England Journal of Medicine in May. More than 40,000 adults 50 and older across 11 countries, including the United States, participated in the Phase 3 study. The trial found mFlusiva was about 27% more effective than the standard-dose vaccine at preventing laboratory-confirmed illness.

FDA reviewers did not identify any serious safety problems with the vaccine during their assessment. Rates of side effects such as injection-site pain, fatigue, and headaches were more common in the mFlusiva group but still mild to moderate. Infectious disease specialist William Schaffner said the higher rate of side effects may be “a reflection of the vigor with which the immune system responds to the vaccine.”

MFlusiva uses a small snippet of genetic code to train the body to recognize and fight the flu virus. “It’s like a temporary instruction to your immune system to alert your body’s natural defense to recognize influenza,” pharmacist Emlah Tubuo said. The mRNA from the vaccine is broken down and does not remain in the body.

The trivalent vaccine targets two influenza A strains and one influenza B strain. It takes about two weeks after vaccination to build protection. MFlusiva does not protect against Covid.

Moderna says mFlusiva can be made in two to three months, while traditional flu vaccines can take about six months to produce. According to the Centers for Medicare and Medicaid Services, mFlusiva has a price tag of around $171 per dose without insurance. Depending on the pharmacy, the cost could be as low as $154, according to GoodRx.

Medicare is required to fully cover the cost of FDA-approved seasonal flu shots. A spokesperson for AHIP said it expects most private insurers will cover the vaccine. The CDC recommends getting vaccinated by the end of October. “If you have not celebrated your 50th birthday, this vaccine should be of no interest to you,” Tubuo said.

Flu season in the United States typically runs from October through March, with peak activity between December and February. The CDC estimates that tens of thousands of people die from flu-related complications each year, with older adults at higher risk for severe outcomes. Annual vaccination is the most effective way to prevent infection and reduce the severity of illness.

Moderna’s mRNA platform, which was used in its Covid-19 vaccine, allows for faster adaptation to circulating flu strains compared to egg-based production methods. This could improve vaccine match and effectiveness in seasons when the virus mutates unexpectedly.

Public health officials are watching uptake of the new vaccine closely, as even small improvements in efficacy can translate into significant reductions in hospitalizations and deaths across the population. The company plans to study mFlusiva in younger age groups in future trials.

Storage requirements for mFlusiva are similar to those of other mRNA vaccines, needing refrigeration between 2°C and 8°C. This makes it compatible with existing vaccine distribution infrastructure, easing integration into current immunization programs.

While the initial supply is limited, Moderna anticipates expanding production capacity in the coming years. The company is also developing a combined mRNA vaccine for flu, Covid-19, and respiratory syncytial virus (RSV), aiming for a single shot to protect against multiple respiratory pathogens.