U.S. approves Moderna's mRNA vaccine for flu—the first of its kind

The flu shot, mFlusiva, was shown in a clinical trial to be up to 27 percent more effective than a standard flu jab

In a first, the U.S. has approved a flu vaccine that relies on mRNA technology—the same technology that underpinned the wildly successful Pfizer-BioNTech and Moderna COVID vaccines.

The approval marks a sea change for the Trump administration. The U.S. Health and Human Services (HHS) Secretary Robert F. Kennedy, Jr., is a vocal critic of mRNA vaccines, and his agency has canceled millions of dollars in funding for mRNA vaccine research. Indeed, the Food and Drug Administration i nitially declined to review Moderna's shot earlier this year, before reversing its decision just a week later.

The vaccine is called mFlusiva and is also made by Moderna. The approval covers two of the most vulnerable populations for flu—adults ages 50 to 65, and adults ages 65 and up—on the condition that Moderna will run a further clinical trial in the older group. Past trial data show that Moderna's vaccine is around 27 percent more effective than a standard flu shot in protecting against the disease.

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For more than 70 years, flu vaccines in the U.S. have been manufactured using one of three techniques: egg-based vaccines (these are the most commonly available), cell-culture based vaccines and recombinant vaccines—these vaccines insert harmless genetic material from the virus into cells in order to trigger the immune system.

Messenger RNA, or mRNA, vaccines work differently. Messenger RNA copies instructions from viral DNA and teaches the body's cells to build and recognize copies of viral proteins. The body can then create antibodies if it should ever encounter that protein again, enabling it to fight off infections.

The other great advantage of mRNA vaccines is that they can be rejiggered quickly to respond to emerging strains of a virus. Traditional flu vaccines are made to protect people from whatever three strains of the influenza virus scientists predict may circulate during the forthcoming flu season. But they have to be made six months in advance of the actual flu season, which means these predictions can fall short of reality. Moderna's new vaccine takes just two to three months to manufacture and roll out.