A group of researchers at the Nebraska Center for Virology may have succeeded in developing a flu vaccine that would provide lifelong protection against the pesky winter bug.

Due to the rapid mutation of the influenza virus, existing vaccines are seasonal; they’re developed based on which flu strains researchers expect will be circulating that year. But the researchers in Nebraska are working to develop a vaccine that uses ancestral genes from four different strains of the flu to provide long-term protection.

For now, the vaccine has only been tested on mice. Nevertheless, the results have been promising. The mice protected with the new vaccine survived exposure to “lethal doses of seven of nine widely divergent influenza viruses.” Those that received higher doses of the vaccine didn’t even get sick, the report says.

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According to estimates by the Centers for Disease Control and Prevention, 40 million Americans suffered from the flu in 2015-16, with 970,000 being hospitalized. Eric Weaver, the lead researcher and an assistant professor at the University of Nebraska-Lincoln, says vaccinations only reduced infections by 4.75% and hospitalizations by 6.9%.

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Conventional vaccines are reportedly less than 60% effective—and that’s only when they’re matched with the currently circulating strain. These statistics demonstrate “that there is a need for more effective vaccine technologies,” Weaver argues.

Ultimately, Weaver and his team hope that one day we will “be able to vaccinate once and provide lifelong protection.” But we’re unlikely to have access to that breakthrough, universal vaccine until 2020 or 2025.