Seasonal flu vaccines can be a bit of a shot in the dark. They protect against the specific influenza viruses researchers predict will be the most common for the upcoming season. You can still catch other varieties of the flu that aren’t among the most common for that year, and flu viruses mutate rapidly, requiring new vaccines every year to protect people. According to one recent study, the protection from a flu vaccine falls after six months. (That's still generally enough time to get most of us through flu season.) 

And so scientists have long been on the lookout for better ways to protect people against the flu. One promising recent lead: a non-vaccine treatment that would make use of cells' natural virus defense mechanisms. A breakthrough approach would be a universal flu vaccine—one that would work against a wide variety of subtypes of influenza, reducing the need for seasonal flu shots.

Two papers released today in two leading science journals, Nature Medicine and Science, indicate that researchers might be inching closer to finding a universal vaccine—one that people could get only once every few years or longer. 

These two studies report success with a vaccine targeting an unusual part of the virus that does not mutate as quickly as other parts, resulting in what’s called heterotypic protection (i.e., protection against a different type of virus than the one the vaccine is designed for). 

Flu vaccines typically raise immunity to one part of the influenza virus called hemagglutinin (HA) glycoprotein. However, HA molecules are different for different influenza strains, and it changes as viruses mutate. 

“We’ve known for some time that there is a region of HA, the stem, that does not change and is present on all flu A viruses, and if we can use only that part in the vaccine we could raise immunity to many different viruses at the same time,” says Sarah Gilbert, an immunologist who studies vaccines at Oxford University, in a statement to the UK's Science Media Centre, “but it has been technically challenging to make a vaccine that works in that way.” 

In Nature Medicine, researchers from the National Institutes of Health were able to protect mice and ferrets against a fatal dose of H5N1 flu, even though the vaccine didn’t result in antibodies that neutralized that particular virus. In Science, researchers from the Janssen Center of Excellence for Immunoprophylaxis (owned by Johnson & Johnson) and the Scripps Research Institute report using antibodies targeting the HA stem to protect mice and monkeys from different flu viruses, including the H5N1 viruses, in lethal doses. 

Creating a universal vaccine would do more than just save people from making the trip to the doctor or pharmacy year after year. Seasonal vaccines don’t protect against the influenza viruses that people get from animals, like swine flu or avian flu. It takes some six months to develop an influenza vaccine, so when a brand new virus comes along like H1N1 did in 2009, scientists have to scramble to catch up, producing a vaccine and getting it into clinics before the virus becomes a pandemic. A universal vaccine would theoretically be better able to protect against new mutations, meaning that people wouldn’t have to wait six months (or more) for protection against a virus that’s already spreading through the population. 

While these studies provide a solid proof-of-concept for vaccines of this type, don’t expect to pick up one of these vaccines at your local pharmacy anytime soon. First, the vaccines will have to make it through human trials, a process that will take years, if they succeed at all.