Getting an mRNA flu shot this season will require some effort, experts say, because supply is limited and distribution has not been fully established. Moderna’s mFlusiva received approval in August for adults 50 and older, arriving long after major pharmacy chains finalized their orders for this year’s standard influenza vaccines. The shot is expected to be available in restricted quantities, according to Amesh Adalja, MD, of the Johns Hopkins Center for Health Security.
Where to Find the Vaccine
Moderna officials confirmed that the company planned a limited launch for the first year. Despite the scarcity, the vaccine is available at more than 13,000 locations, according to a Moderna spokesperson who provided a link to the company’s vaccine finder. Adalja noted that patients will likely need to use that website or call around to pharmacies to locate the product.
The search for mFlusiva mirrors the early days of the Flublok vaccine, which Adalja prefers. During that period, he had to call various pharmacies to track down the product because drugstores often order the standard formulation and do not differentiate between vaccine types. Flublok and Flucelvax, other novel vaccines, faced similar distribution challenges in the past.
Types of Flu Vaccines
Several vaccine options exist for the upcoming season. Standard-dose products, typically grown in eggs, include Fluzone, Fluarix, FluLaval, and Afluria. An egg-based live-attenuated nasal spray, FluMist, is also available. For those seeking enhanced protection, there are recombinant and cell-based egg-free options. Flublok, a recombinant vaccine, contains three times the antigen of standard doses, while Flucelvax is a cell-based alternative.
Other enhanced vaccines, such as Fluzone High-Dose and the adjuvanted Fluad, are approved for individuals 65 and older. These products are still produced in eggs. The newly approved mRNA shot adds another option to this list.
Regulatory Path and Data
The FDA approved the mRNA flu shot with traditional approval for adults 50 to 64 and accelerated approval for those 65 and older. This distinction included a requirement for a postmarketing effectiveness study in the older population. The agency initially refused to review Moderna’s application because it lacked a better comparator than a standard-dose vaccine. A week later, the decision was reversed.
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One phase III study did demonstrate that the mRNA shot generates a greater immune response than Fluzone High-Dose in adults 65 and up. However, the trial did not measure clinical outcomes like preventing illness. William Schaffner, MD, of Vanderbilt University, noted that while the immune response is superior, it remains unclear if that translates to better protection against the virus.
Adalja acknowledged that head-to-head studies comparing mFlusiva to other enhanced vaccines are lacking. He stated that he considers Flublok or mFlusiva the two best options available, though this assessment is based on data interpretation rather than direct clinical comparisons. The CDC determined that the B/Yamagata influenza lineage had stopped circulating after March 2020, leading to the switch to trivalent vaccines for everyone.
Side Effects and Availability
People must weigh the benefits against the side effects. Schaffner noted that the mRNA vaccine causes higher reactogenicity than standard flu shots. Common reactions include injection-site pain, fatigue, headache, and myalgia. Adalja suggested that healthcare workers might hesitate to get the shot if they are concerned about missing shifts due to these reactions.
There is a theoretical advantage to the mRNA platform, according to Schaffner. Because the technology is adaptable, it could potentially allow for a faster match to circulating strains. FDA finalizes strain selection in March, but newer technologies could shorten this timeline. However, implementing this change would require a significant shift in policy frameworks used by the FDA and the World Health Organization.
Regardless of the technical details, Schaffner emphasized that vaccination should happen now. Influenza activity has started early in many parts of the country. If you have not been vaccinated, run, do not walk … and get the vaccine that’s available to you.
