Just as GlaxoSmithKline nears a decision from the U.S. FDA for its key shingles vaccine, Shingrix, Canada has become the first country to approve the shot—and it's a key piece of CEO Emma Walmsley's prescription for growth at the drugmaker.

The Canadian approval covers people 50 years or older, as a prevention tool against the painful condition that's caused by latent varicella infection. It's based on a phase 3 trial that involved 37,000 people, 2,100 of whom were enrolled at 31 sites across Canada.

The two-pronged study showed that the recombinant, adjuvanted vaccine, given in two doses two to six months apart, is 97.2% efficacious in the target population and maintained a 90% efficacy in those 70 and above for at least four years.

"As we age, our immune system loses the ability to mount a strong and effective response to infection," GSK's vaccines CMO, Thomas Breuer, M.D., said in a statement. "Shingrix was developed specifically to overcome the age-related decline in immunity."

The results also helped GSK's shot win a unanimous recommendation from an FDA advisory panel just last month. The agency doesn't always follow its committees' recommendations, but it usually does, setting the shot up for approval this year. Shingrix is one of three key launches new GSK CEO Emma Walmsley says are a near-term focus for the drugmaker.

Based on its efficacy and safety profile, plus shingles' incidence and the severe pain associated with the infection, life science commercial intelligence firm Evaluate recently predicted Shingrix will reach blockbuster status by 2022.

Although investigators haven't conducted head-to-head tests, one expert on the FDA panel said Shingrix is "a lot better than the vaccine we have now," referencing Merck’s Zostavax, the only approved shingles shot, which has had the market to itself since 2006. The one-dose vaccine can reduce the risk of developing shingles by 51%, according to the CDC, and lower the risk of postherpetic neuralgia by 67%.

About 1 in 3 people develop shingles in their lifetimes. GSK said shingles affects about 130,000 Canadians annually, and the CDC estimates that 1 million cases of shingles occur in the U.S. each year. The risk increases with age, with about half of all cases occurring in people 60 years or older. Incidence rates in Europe and the Asia-Pacific region are similar, according to the company.

The CDC’s Advisory Committee on Immunization Practices, which recommends vaccination policy for the agency, will also vote on Shingrix this month. GSK is additionally seeking approval in Europe, Australia and Japan.