Studies have shown that a new universal flu vaccine can prevent deaths and reduce the symptoms of different influenza strains in lab animals.

Developed by two independent teams of researchers, the vaccine works by targeting a stable part of the flu virus, which means one injection could replace the seasonal vaccinations we have now, and this could protect us against all of the most dangerous strains, including the potentially pandemic ones that spread from pigs and birds to humans. 

Right now, we have no choice but to re-up our flu vaccination every year because it works by targeting a part of the flu virus that's constantly mutating - the 'head' of the lollipop-shaped haemagglutinin (HA) molecules that coat the surface of the virus. 

Not only does this part of the molecule mutate from season to season in the same flu strain, which is why you have to get a reformulated jab each year to stay protected, it differs across existing and emerging flu strains. This means our current vaccines aren't always effective - last year's seasonal flu vaccine reduced the need to see a doctor by just 23 percent - they're also constantly out of step with the potentially deadly strains that are being transferred from farm animals to humans.

"During the last flu season, mutations in the HA molecule on one of the most common circulating strains, H3N2, meant that the seasonal flu vaccine offered little protection," Ian Sample writes at The Guardian. "Public Health England said in February that the less effective vaccine was likely to have been behind a steep rise in flu deaths."

This new vaccine, on the other hand, targets a part of the HA molecule that changes far less rapidly than the head. Described in separate papers in Science and Nature Medicine this week, the vaccine targets the 'stem' of the molecule, which mutates far slower across seasons and strains than the head.

This might sound like an obvious fix, but developing a vaccine that targets the stem has been no small feat. An antibody that binds to the HA stem instead of the head was only discovered back in 2008, and when scientists built these antibodies into a vaccine, they couldn't figure out how to make the body's immune system ignore the head and go for the stem.

One team, from the US National Institutes of Health, got around this problem by attaching parts of the HA stem to another protein called ferritin. When the vaccine was injected, the protein served a type of 'glue' that kept the stems together and also highlighted their presence to the body's immune system so they could be targeted.

The other team, from the Crucell Vaccine Centre in the Netherlands, included an altered version of the flu in their vaccine by chopping the heads off the HA molecules and modifying the stem so the antibodies could bind to them more effectively. 

"Both HA proteins modified from the swine flu virus could protect mice infected with, importantly, a second strain (H5N1 or avian flu) from losing weight through illness," Sarah Zhang reports for Wired. "The nanoparticles also saved four out of six ferrets from dying of avian flu. (The untreated ones all died.) The mini-HA reduced fever in five swine flu-infected monkeys and elicited antibodies that could bind to the avian flu."

The next step will be to get both versions of the vaccine to human trials to see if these results can be replicated, and unfortunately, that will likely take several years. And then researchers will also have to figure out how to apply it to the vast array of flu strains to make it truly 'universal', as Zhang explains:

"The highest level of classification divides the viruses into influenza A, B, and C; A includes all the biggest troublemakers. Within influenza A are group 1 and group 2, sorted based on which HAs are expressed on the viral surface. On top of that, 16 different HA subtypes mix and match with nine subtypes of another protein called neuraminidase to create strains such as H3N2 or H5N1."

So far, the teams have been working on group 1 strains from the influenza A group, but seeing as these are the worst ones, having a vaccine that just covers those would be incredible. We'll just have to wait and see if they can get there.