Two years ago, when the first COVID-19 vaccines were administered marked a game-changing moment in the fight against the pandemic. But it also was a significant moment for messenger RNA (mRNA) technology, which up until then had shown promise but had never quite broken through. 

Now, scientists hope to use this technology to develop more vaccines, with those at the University of Pennsylvania hoping to use that technology to pioneer yet another first: a universal flu vaccine that can protect us against all flu types, not just a select few. 

It’s the latest advance in a new age of vaccinology, where vaccines are easier and faster to produce, and more flexible and customizable. 

“It’s all about covering the different flavors of flu in a way the current vaccines cannot do,” says Ofer Levy, MD, PhD, director of the Precision Vaccines Program at Boston Children’s Hospital, who is not involved with the UPenn research. “The mRNA platform is attractive here given its scalability and modularity, where you can mix and match different mRNAs.” 

A paper published in  Science  reports successful animal tests of the experimental vaccine, which, like the Pfizer-BioNTech and Moderna COVID vaccines, relies on mRNA. But the idea is not to replace the annual flu shot. It’s to develop a primer that could be administered in childhood, readying the body’s B cells and T cells to react quickly if faced with a flu virus. 

It’s all part of a National Institutes of Health-funded effort to develop a universal flu vaccine, with hopes of heading off future flu pandemics. Annual shots protect against flu subtypes known to spread in humans. But many subtypes circulate in animals, like birds and pigs, and occasionally jump to humans, causing pandemics. 

“The current vaccines provide very little protection against these other subtypes,” says lead study author Scott Hensley, PhD, a professor of microbiology at UPenn. “We set out to make a vaccine that would provide some level of immunity against essentially every influenza subtype we know about.” 

That’s 20 subtypes altogether. The unique properties of mRNA vaccines make immune responses against all those antigens possible, Hensley says. 

Old-school vaccines introduce a weakened or dead bacteria or virus into the body, but mRNA vaccines use mRNA encoded with a protein from the virus. That’s the “spike” protein for COVID, and for the experimental vaccine, it’s hemagglutinin, the major protein found on the surface of all flu viruses.

Mice and ferrets that had never been exposed to the flu were given the vaccine and produced high levels of antibodies against all 20 flu subtypes. Vaccinated mice exposed to the exact strains in the vaccine stayed pretty healthy, while those exposed to strains not found in the vaccine got sick but recovered quickly and survived. Unvaccinated mice exposed to the flu strain died. 

The vaccine seems to be able to “induce broad immunity against all the different influenza subtypes,” Hensley says, preventing severe illness if not infection overall. 

Whether it could truly stave off a pandemic that hasn’t happened yet is hard to say, Levy cautions. 

“We are going to need to better learn the molecular rules by which these vaccines protect,” he says.

But the UPenn team is forging ahead, with plans to test their vaccine in human adults in 2023 to determine safety, dosing, and antibody response. 


Ofer Levy, MD, PhD, director, Precision Vaccines Program, Boston Children’s Hospital. 

Scott Hensley, PhD, professor of microbiology, University of Pennsylvania. 

Science: “A multivalent nucleoside-modified mRNA vaccine against all known influenza virus subtypes.” 

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