Year after year, scientists have been coming up with flu vaccines that protect against a few specific strains of influenza. These strains are those predicted by research to be the most common during the following year. There is new reason to believe, however, that scientists will be able to create a more universal vaccine soon, one that can protect against many more strains of influenza, including those that could cause future epidemics.

"The reason researchers change the vaccine every year is that they want to specifically match the vaccine to the particular viruses that are circulating, such as H1N1,” said principal investigator of the study Dr. Jeffery Taubenberger, chief of Viral Pathogenesis and Evolution Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases (NIAID) in a press release. “If the vaccine is just a little bit different to the target virus, it is not expected to offer much protection. What we have done is design a strategy where you don't have to think about matching the vaccine antigen to the virus at all."

In the study, researchers created a sort of vaccine cocktail that contained a veriety of different subtypes of a key surface protein of the influenza virus — hemagglutinin H1, H3, H5 and H7.

"There are 16 different hemagglutinin subtypes that circulate in birds and are thought to be the basis for current and future influenza pandemics," Taubenberger said. "The hypothesis was that the presentation of these different viral proteins would stimulate the development of cross-protective immunity that would provide broader protection against multiple subtypes."

The H1 and H3 subtypes were chosen by researchers because of their frequency in the past — they have been the biggest cause of human seasonal flu outbreaks since 1918. They chose H5 and H7 because they have been heavily involved in bird outbreaks, and have the potential to cause pandemics. These selections also provided a comprehensive representation of subtypes.

The study compromised a series of experiments in which mice were exposed to a lethal combination of eight different influenza strains. Ninety-five percent of the mice who had first been injected with the experimental vaccine cocktail were protected against the strains. Only five percent of the mice who did not receive the vaccine avoided infection.

"Almost all of the animals that were vaccinated survived, including mice that were challenged with viruses that expressed hemagglutinin subtypes that were not in the vaccine at all, viruses that expressed H2, H6, H10, and H11," Taubenberger said. "What that suggests is that this approach really gives us broad spectrum protection, and could serve as a basis for an effective pre-pandemic vaccine."

Further experiments showed that the vaccine was effective for at least six months, and was effective in older mice. This is key, since the elderly are especially vulnerable to influenza, and current vaccines are less effective on them than on younger patients.

"These initial findings are very positive and suggest a promising and practical strategy for developing a vaccine with amazing, broad protection," Taubenberger said.

Source: Schwartzman L, Cathcart A, Pujanauski L, Qi L, Kash J, Taubenberger J. An Intranasal Virus-Like Particle Vaccine Broadly Protects Mice From Multiple Subtypes of Influenza A Virus. mBio. 2015.