A "headless" version of the influenza virus protected mice from several different strains of flu and may offer a step toward a so-called universal flu vaccine, researchers report.
They identified a piece of the virus that appears to be the same even among mutated strains, and found a way to make it into a vaccine.
Years of work lie ahead but if it works in people the way it worked in mice, the new vaccine might transform the way people are now immunised against influenza, the team at the Mount Sinai School of Medicine in New York reported.
"We now report progress toward the goal of an influenza virus vaccine which would protect against multiple strains," Dr Peter Palese, Dr Adolfo Garcia-Sastre and colleagues report in a new journal mBio.
"Current influenza vaccines are effective against only a narrow range of influenza virus strains. It is for this reason that new vaccines must be generated and administered each year."
Flu constantly changing
Flu viruses mutate constantly and each year a cocktail of three flu vaccines is tweaked to try and hit the most common new mutations. Every few decades a new pandemic strain emerges - a year ago the new H1N1 swine flu strain started a pandemic and it has been added to the seasonal flu vaccine mix.
It takes months to make a new flu vaccine and governments and commercial drug companies struggled to get the new H1N1 vaccine out by last September. Having a universal flu vaccine could, in theory, prevent future pandemics and keep seasonal flu under better control.
Palese's team focused on an important piece of the flu virus called haemagglutinin. This mushroom-shaped structure helps the virus attach to the cells it infects and gives flu viruses the "H" in their names.
The "neck" of haemagglutinin does not mutate the way more visible bits of the virus do, and if there was an easy way to help the immune system to see it, this provides a good antigen - a target for a vaccine.
What the study revealed
But the top, umbrella-shaped part of the hemagglutinin protein hides this vulnerable neck from the immune system. Palese's team found a way to get to the neck, cut it out and make a vaccine out of it.
"A headless haemagglutinin molecule could form the basis for a broadly protective influenza virus vaccine," the researchers wrote.
"This paper is more proof of concept," Garcia-Sastre said. "We don't think we have yet the most optimal way to display the antigen."
Tests in mice showed the vaccine protected them from otherwise lethal doses of multiple strains of influenza.
Garcia-Sastre's team made a plasmid, a circular piece of DNA, for their vaccine but other ways to do it include a virus-like particle, used in other vaccines, or bits of DNA made by a baculovirus, he said. He said they are open to working with a drug company on this.
Flu infects up to 10 to 15% of the US population each year, more in a pandemic year, and kills an estimated 36 000.
Dozens of companies make influenza vaccines and bring in millions of dollars in revenues from them. The United States, for instance, bought 162 million doses of H1N1 vaccine from five makers - Novartis, AstraZeneca unit MedImmune, Sanofi Aventis, GlaxoSmithKline and Australian vaccine maker CSL. - (Reuters Health, May 2010)