With hope for saving millions of lives around the world, scientists may soon develop a universal vaccine for the influenza virus — a single shot for every strain.

Researchers at Imperial College London say they’ve drawn a “blueprint” for a universal vaccine capable of targeting the core proteins within the virus, representing a leap forward in the cat-and-mouse game between virus and vaccinologist. As influenza changes proteins on the surface of virus strains to evade new vaccines, the universal vaccine — potentially available within five years — would eliminate the need for new seasonal flu vaccines every year.

In the study, the researchers used the 2009 swine influenza, a recombinant of swine and avian flu, to test a theory that T-cells within the immune system recognize proteins at the virus’s core. To do so, they compared a specific type of T-cell with influenza symptoms in 342 staff members and students at the university, finding that those with milder symptoms of disease showed higher levels of T-cells. Subsequently, they identified the specific part of the immune system offering some protection from pandemic influenza, in addition to which part of the virus conducted the attack.

“It's a blueprint for a vaccine,” lead investigator Ajit Lalvani told the BBC. “We know the exact subgroup of the immune system and we've identified the key fragments in the internal core of the virus. These should be included in a vaccine.”

Lalvani said researchers might produce the universal vaccine within five years. “We have the know-how, we know what needs to be in the vaccine and we can just get on and do it,” he said.

The novel approach to viral counterattack differs from traditional vaccines, such as the measles, mumps, and rubella shot, which provokes the immune system into producing antibodies against the virus. It’s also harder to do. Scientists must now develop a T-cell vaccine capable of provoking a strong enough response in the immune system, according to John Oxford, a professor at Queen Mary University of London.

“This sort of effect can't be that powerful or we'd never have pandemics. It's not going to solve all the problems of influenza, but could add to the range of vaccines,” Oxford told the BBC. "It's going to be a long journey from this sort of paper to translating it into a vaccine that works."

Researcher Sarah Gilbert, of the Jenner Institute in Oxford, likewise expressed caution regarding the challenge of moving from research to development. "Live attenuated influenza vaccines which are given by nasal spray and will be used in children in the [United Kingdom] from this autumn are much better at increasing the number of influenza-specific T cells," she said, "but these vaccines only work in young children who haven't yet had much exposure to influenza virus, so we need an alternative approach for adults."

However, she said that the new research would provide useful information about “precise characteristics” of T-cells protective against influenza, helping researchers monitor immunological response when testing vaccines for pandemic and seasonal influenza viral strains.

The promise looms large. Seasonal strains of influenza kill between a quarter-million and a half-million people every year around the world, with the specter of a global pandemic capable of killing millions.