Researchers think they've taken a solid step towards making a better flu vaccine by fiddling around with the genetics of flu viruses.
Current flu vaccines are not very good, experts agree.
They only reduce illness by between one third and two thirds, although they do prevent death and they do keep many people from becoming sick enough to need hospitalization.
The problem is that flu viruses mutate all the time. They mutate as they circulate among people, and they alsomutate in the process of using them to make vaccines — which can make the vaccine less effective than it should be.
These changes help explain why people need a new flu vaccine every year.
Plus, in any one season three to four strains could be circulating and making people sick, which is why vaccines protect against three or four strains — H1N1, H3N2 and either one or two B strains.
Flu vaccine researchers are trying to find parts of the flu virus that don't mutate so they could use it to make a better vaccine. But a team led by Ren Sun at the University of California Los Angeles decided to go the other way and make use of the virus's tendency to mutate.
They mutated flu viruses even more, and came up with a version that was especially vulnerable to the body's immune system. At the same time, it was a very wimpy virus and did not spread well in the body.
The mutations made the virus very susceptible to immune system signaling proteins called interferons.
Sun's team made it into what's called a live attenuated vaccine. That is a common vaccine approach, in which a virus is weakened so that it doesn't make people sick, but still alive so that the body's immune system recognizes it and gears up to fight it on several fronts.
Tests in mice and ferrets — which catch flu in very much the same way that people do — showed the interferons could not only kill this particular flu virus easily; the body also produced a lot of them in response to the vaccine.
The vaccine should work against various strains of influenza, something that current vaccines cannot do. Right now, the annual flu vaccine is a cocktail that protects against either three or four different strains of flu. A so-called universal flu vaccine would protect against many or even all strains of flu and would, ideally, protect people for longer than just one year.
This new approach may also work against other viruses, the researchers said.
"Our approach, which attenuates the virus and promotes immune responses concurrently, is broadly applicable for vaccine development against other pathogens," Sun and colleagues wrote in their report, published in the journal Science.
"Using some neat genetic engineering, the researchers were able to generate a severely disabled virus that was still able to infect animals without causing symptoms, even at really high doses," said molecular virologist Jonathan Ball of the University of Nottingham, who was not involved in the research.
"Crucially, this virus was able to provoke strong immunity - much better than an existing disabled flu vaccine virus - that could protect against infection by different strains of influenza virus. A vaccine that can produce potent and cross-reactive immunity should be able to protect us against the different strains of virus that emerge in new seasonal influenza epidemics, something that current vaccines struggle to do."
It takes a long time to develop new flu vaccines and what works in animals may not work in humans.
There are several different types of flu vaccines on the market now, but none can protect against multiple strains of flu.
Vaccine makers have been cautious about investing in new vaccine technology. It can take years to develop a vaccine and the factories where they are made are subject to stringent requirements of safety and cleanliness. Plus, it's an uncertain market. Every year, the CDC says everyone 6 months old and older should get a flu vaccine, but every year, not even half of people do.
Every year, some doses of flu vaccine get thrown away.