Results from two new major studies suggest that scientists are even closer to their ultimate goal of creating a universal flu vaccine that can provide a lifetime of protection with a single shot. Although clinical trials are needed before the vaccine becomes available, such a shot could potentially save thousands of lives from the common yet deadly virus each year.

Many vaccines, such as those for hepatitis and the chicken pox, offer patients a lifetime of protection against the target virus with just one shot. Flu vaccines, however, must be readministered each season in order to provide optimal protection. For years now, researchers have been working on creating a universal flu vaccine that would provide protection with just a single jab. Results from two recent studies published in the online journals Science and Nature showed that current candidates for this long-lasting vaccine are highly effective in providing animals with universal flu protection — a clear sign that scientists are doing something right.

The flu virus’s structure is unique. While its interior, or “stem,” stays consistent, the molecules on its outer surface constantly change. Current flu vaccines work by targeting these outer molecules, and as a result need to be updated each year to keep up with the virus’s constant mutations. In theory, the universal vaccine would target the consistent “stem” of the flu virus, BBC News reported. However, this feat is easier said than done, and scientists have found it particularly difficult to create a vaccine that does not involve the outer molecules.

"They have good animal data, not just in mice but in ferrets and monkeys too. And they've done it with the bird flu virus H5N1," John Oxford, a flu expert at the University of London told BBC News. "It's a very good stepping stone. Ultimately, the hope is to get a vaccine that will cover a pandemic virus."

The next step for the vaccine prototypes would be human clinical trials, a process that could take several years. In the meantime, individuals are advised to continue receiving annual flu shots to protect themselves as flu season quickly approaches.

On a global scope, the flu is a very deadly virus. According to the World Health Organization, each year the flu causes an estimated three to five million cases of severe illness and kills a reported 250,000 to 500,000 individuals. In addition to the human toll, flu epidemics can cause a significant loss of workforce productivity and a strain on health services.

Yearly flu epidemics can seriously affect all populations, but those at the highest risk of hospitalization and death are young children, seniors, pregnant women, and people of any age with particular health conditions. Currently, the WHO recommends annual flu vaccines as the most effective way to prevent either contracting the virus or preventing severe outcomes from the illness.

Source: Impagliazzo A, Milder F, Kuipers H, et al. A stable trimeric influenza hemagglutinin stem as a broadly protective immunogen. Science. 2015.

Yassine HM, Boyington JC, McTamney PM, et al. Hemagglutinin-stem nanoparticles generate heterosubtypic influenza protection. Nature Medicine. 2015.