The new mRNA flu shot mFlusiva is more effective. Why doctors worry Long Islanders may not try it.

A newly approved flu vaccine that studies show is more effective than others may be in Long Island pharmacies in the coming weeks, but the mRNA technology it uses may unnecessarily scare some people away from using it, medical experts say.

The Food and Drug Administration Wednesday approved Moderna’s mFlusiva for people ages 50 and older after a study of more than 40,000 people ages 50 to 64 showed it is 26.6% more effective than a regular-dose traditional flu vaccine in preventing symptoms.

FDA approval is only for people 50 and older; approval for those 65 and older is provisional while further studies are conducted. Moderna also is studying mFlusiva in younger adults and adolescents.

Most years, tens of thousands of people — most of them older adults — die of the flu and hundreds of thousands are hospitalized.

MFlusiva, like the COVID-19 vaccine developed by Moderna and others, uses messenger mRNA, which are molecules found in all human cells.

MFlusiva is only the second FDA-approved mRNA vaccine, after the one for COVID. To show "we can use it for other very common diseases, that’s a great new confirmation," said Dr. Martín Bäcker, a principal investigator at the NYU Langone-Long Island Vaccine Center. "We anticipated it would work. But you don’t know how well it can work compared with traditional vaccines until you do the studies."

MFlusiva has the potential to save many lives because it can more closely match the most commonly circulating flu strains each season, said Dr. Sharon Nachman, chief of pediatric infectious diseases at Stony Brook Medicine.

Each spring, scientists look at which influenza strains are causing illness in the southern hemisphere's flu season and pick which ones they believe will be most dominant in the fall, she said.

"Some years we guess right and some years we guess not so right," Nachman said.

Most flu vaccines are developed today just as they were more than 70 years ago: Growing vaccine viruses in chicken eggs, which is why the process is so time-consuming.

"The ability to make a flu vaccine in real time that matches the circulating flu strains is going to be a game changer," Nachman said.

mRNA vaccines use the genetic sequence of a virus to prepare the body to fight an infection.

"It’s called a messenger for a reason," said Jeff Coller, a professor of RNA biology and therapeutics at Johns Hopkins University in Baltimore who has researched messenger mRNA for more than 30 years. "It’s communicating information." 

The potential to save many lives — and prevent serious illness or any symptoms at all — is especially high in flu seasons when traditional vaccines don’t match the most dominant strains, said Dr. Bruce Farber, chief of public health and epidemiology at Northwell Health.

"It could be dramatically more effective" those years, he said.

One of the biggest problems will be convincing people to take it, he said.

Vaccine distrust, bumpy approval

Although experts estimate COVID vaccines saved more than three million American lives, only 56% of Americans believe it is safe, a survey by the health nonprofit KFF found last year.

False claims that began during the pandemic that mRNA vaccines alter DNA persist, with about a quarter of the public believing that.

Flu vaccination rates, while never high, have slipped in recent years to only about 48% of New Yorkers for the 2024-25 flu season, a KFF analysis found. 

Farber said that, with rampant misinformation about mRNA vaccines, some people will never trust them, but over time, more people likely will become comfortable with them.

Misinformation almost prevented the new flu vaccine from being reviewed at all, Coller said.

In February, the FDA refused to consider Moderna’s application for mFlusiva until an outcry by scientists and the drug industry led the agency to reverse itself.

HHS Secretary Robert F. Kennedy Jr. is a longtime skeptic of vaccines and mRNA technology, and when HHS canceled $500 million in mRNA research projects in August of last year, he claimed they aren’t effective against diseases like the flu and COVID.

The statement, which came more than a month after Moderna released its data showing mFlusiva’s effectiveness, "is completely contrary to the evidence," Coller said.

Kennedy’s skepticism of mRNA vaccines can have huge consequences, because of their potential to save countless lives, he said.

Moderna announced Tuesday it is beginning the first human trial of an mRNA vaccine against a particularly deadly strain of the Ebola virus, and studies have shown promising results from clinical trials for mRNA cancer vaccines. 

HHS did not respond directly to questions on the initial refusal of the FDA to consider Moderna’s application and on Kennedy’s comments against mRNA technology.

But HHS spokeswoman Emily Hilliard said in an email that "Secretary Kennedy has been clear that he believes mRNA products warrant heightened scientific scrutiny."

The vaccine approval for those 65 and older was conditional on further research, and "HHS will continue to follow the evidence and make safety and effectiveness data publicly available as additional information emerges," Hilliard wrote.

By David Olson

david.olson@newsday.com@DavidOlson11

David Olson covers health care. He has worked at Newsday since 2015 and previously covered immigration, multicultural issues and religion at The Press-Enterprise in Southern California.