Scientists are getting closer to developing a vaccine that protects against multiple types of flu viruses, according to two separate studies published today in Nature Medicine and in Science.

The new vaccines generated strong immune system responses against the deadly H5N1 "bird flu" and the H1N1 virus in mice, ferrets, and monkeys, according to the Associated Press. If the techniques used to make these vaccines can be applied to human vaccines, these drugs could provide broad protection against multiple flu strains — perhaps even against some that have yet to emerge.

Current flu vaccines have to be reformulated each year

Current flu vaccines have to be reformulated each year to suit the latest, most prominent strain. These new vaccines would remove the guesswork involved in predicting which strain will dominate the flu season. That's because they work by mimicking a stable part of the virus that doesn't change from one season to the next. Researchers have known about this vaccine target for a few years now, but until recently, they hadn't been able to produce a vaccine that provoked the appropriate immune response. Now, scientists have demonstrated that it is possible, at least in animals.

In theNature Medicine study, researchers administered a vaccine to mice and ferrets. Then, they infected the animals with the H5N1 virus — a virus that kills more than 50 percent of the humans it infects. They found that all the mice and most of the ferrets developed full immunity against the virus.

The vaccine in the Science study was just as effective in mice. When it was used on monkeys, the researchers found that it triggered a strong immune system response and reduced the fever of the monkeys they injected with H1N1 — a very contagious, but less deadly strain.

The vaccines triggered an immune response in ferrets, mice, and monkeys

"The approach being developed here... does offer the potential of a 'universal' influenza vaccine," Walter Orenstein, a vaccine researcher at Emory University told the Genetic Expect News Service of the Nature Medicine study. But he cautions that these are animal studies, which means that "we are some way off for development and testing of a vaccine in humans."

It may be a number of years before a candidate "universal" flu vaccine is tested on humans. Ferrets and monkeys are very different from humans, so scientists will have to find a way to adapt their vaccines to meet human needs. Still, the fact that this worked at all is a step in the right direction. Perhaps one day humans will only need to be vaccinated once, instead of every year.