Researchers are hopeful that the success of those coronavirus vaccines will grease the wheels for mRNA flu shots and help expedite what is typically a lengthy process involving years of research, clinical trials and regulatory review and approval.
“It’s a very obvious progression given the success of the covid-19 vaccine to move right to flu,” said Andrew Pekosz, a professor of microbiology at the Johns Hopkins Bloomberg School of Public Health.
But researchers say the development and approval of an mRNA flu shot may take some time.
The idea that scientists can use messenger RNA for medical therapeutics is not new. Flu shots using mRNA technology have been in development for years.
But using mRNA for vaccines shifted from experimental to critical last year. With a pressing need spurred by a global pandemic and billions of dollars in funding for vaccine development, scientists were able to repurpose their knowledge of mRNA to develop coronavirus vaccines.
“People who were slogging away for many years had money thrown at them to get it done. And they became laser-focused to bring something to market that would have ordinarily taken years,” said Paul Duprex, director of the Center for Vaccine Research at the University of Pittsburgh.
Currently, the most common influenza vaccine that is available in the United States is manufactured using an inactivated, or killed, virus and administered via a shot in the arm. But there is also a vaccine that uses a live, but weakened, virus and is given in the form of a nasal mist.
The flu viruses for these vaccines are grown in chicken eggs or in cells inside a petri dish. The viruses are then killed or weakened, and the resulting proteins — the important ingredient in the vaccine — are purified. When the shot is administered, the immune system starts making antibodies against those proteins.
“But the mRNA vaccine is very, very different,” Pekosz said, explaining that mRNA vaccines can teach the immune system to fight a virus without ever coming into contact with it. They can also “generate a much stronger immune response than responses that are generated to the protein in a normal flu vaccine,” he added.
One limitation of the current flu vaccines is that they take about six months to develop, meaning scientists must choose which strains they think will be prevalent in the next flu season — even before the current one is over. So by the time the vaccines are ready for distribution, a different strain may have emerged as the better target.
An mRNA flu vaccine, on the other hand, can be developed in about a month or so, giving researchers plenty more time to determine which strains to protect against.
All of this means “you can much more accurately match an mRNA flu vaccine to the strains of virus that are circulating,” Pekosz said.
Messenger RNA vaccines still present challenges. The Pfizer and Moderna coronavirus vaccines, for example, must be kept at extremely cold temperatures, making transport and storage a challenge. It’s also not clear how long this vaccine-induced immunity will last. And although most side effects to the vaccine are not serious, some people have reported several days of things such as fatigue, body aches and nausea as their immune systems gear up to attack the coronavirus.
Still, researchers say mRNA vaccines are a success. And because the mRNA vaccine platform that was used for the coronavirus vaccines is almost exactly the same platform needed for the flu, “everything that has worked so beautifully for covid-19 could theoretically work in exactly the same way for influenza,” Pekosz said.
Researchers say mRNA flu shots are not likely going to be developed and approved in time for the upcoming flu season, and some researchers estimate that it could take several more years to get one on the market.
Even then, it will likely be a phased rollout with both traditional flu shots and mRNA flu shots available, Duprex said.
“It will be gradual,” he said. “You just don’t change technology overnight.”