It’s not necessarily obvious which part of the flu virus any potential mRNA vaccine should target. “You have to make sure you’re targeting the right part of the virus,” Scher says. With Covid-19, the prominent spike protein fit the bill. But flu viruses are arguably more complicated and mutate more quickly, meaning if you choose the wrong protein, your shot could be less effective than expected. The flip side, Scher suggests, is that mRNA vaccines could make it possible to target multiple proteins or parts of proteins in the same virus, a multifaceted strategy.
And while they are difficult to develop, the speed with which mRNA vaccines can be produced could be enormously beneficial. Traditionally, flu vaccines contain inactivated viruses that are grown in chicken eggs. This works reasonably well, but it takes a long time to make such injections, meaning health authorities have to publish their predictions about which flu strains will circulate during the coming winter well in advance. If vaccines could be made more quickly, more accurate predictions could be made when flu season approaches.
Not only that, researchers hope that a single injection of mRNA could one day attack 20 or more flu strains at once, alleviating the need for some of this guesswork. Scher’s colleagues are working on such a “universal” flu vaccine.
With clinical trials underway, it’s still early days. Sheena Cruickshank, an immunologist at the University of Manchester, has watched reports of emerging mRNA flu shots with interest, but says doubts remain. “We still don’t know how long-lasting the immunity they produce is,” he says.
Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, agrees, although he notes that all flu vaccines, regardless of how they are made, have a problem of waning immunity: Their protection could be diminished. . by about 10 percent each month after injection.
A specific concern with mRNA vaccines is that they tend to cost more than traditional flu vaccines and must be kept refrigerated, which can make them difficult to roll out in areas with poor infrastructure. Researchers are also concerned that they may find more vaccine hesitancy. “The mRNA vaccine platform, per se, is probably the one that seems to get the most misinformation,” Cruickshank says. “That could be a disadvantage.”
A new wave of mRNA flu vaccines could have a particular impact for older patients, says Jenna Bartley, an assistant professor at UConn Health, a health and hospital research center. Older people are among those most at risk of contracting the flu, but current vaccines are less effective in older age groups as their immune response tends to be weaker. However, Covid-19 mRNA injections have been shown to be effective in older people as well as the youngest.
It may be some time before mRNA shots are available for seasonal flu. However, if H5N1 starts infecting many more people, and especially if we find that it is frequently transmitted between humans, there is a chance that an mRNA vaccine against bird flu could be the first such vaccine deployed on a large scale. U.S. health officials have said that an H5N1 mRNA vaccine could be available in a few weeks, if necessary.
Osterholm agrees that time frame is realistic. The real challenge, he notes, would be getting any new H5N1 vaccine to the people who need it most. Covid-19 shots emerged in rich countries and were given to people very quickly, he says, but “in much of the world, that was not the case at all.”
