What Zostavax? GSK's Shingrix eclipses Merck shingles shot with massive market-share steal

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GlaxoSmithKline’s Shingrix has surpassed Merck's Zostavax, nabbing 90% of the U.S. shingles vaccine market. (FiercePharma)

GlaxoSmithKline's Shingrix is on track to rule the U.S. shingles vaccine market once monopolized by Merck & Co.’s Zostavax, just five months after it was approved by the FDA.

By mid-March, the GSK shot had staked out a huge chunk of the shingles-shot field, according to an IQVIA tally based on about half of all prescriptions. As cited by a Monday note from Deutsche Bank analysts, Shingrix scripts accounted for 90% of that IQVIA universe. Meanwhile, Zostavax prescriptions over the same period plummeted by more than 80%.

It now begs the question: Will GSK eventually push Merck out of the U.S. shingles market, just as Merck’s Gardasil family of HPV shots once drove away Glaxo's Cervarix?

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That, of course, remains to be seen. What's evident now is that Shingrix has made a swift market grab, and it probably has a CDC recommendation to thank for that feat, at least partly. After an Advisory Committee on Immunization Practices’ decision in October, the CDC officially recommends Shingrix over Zostavax to prevent herpes zoster. Plus, the agency expanded its shingles vaccine recommendation to cover adults 50 and older, rather than 60 and older—and recommends Shingrix even for people already vaccinated with Zostavax. That's quite a recommendation: GSK estimates that it gives Shingrix a market of 100 million people in the U.S. alone.

RELATED: GlaxoSmithKline's Shingrix launch gets a jump-start with CVS move to stock thousands of pharmacies

It doesn't hurt that Glaxo moved Shingrix into pharmacies quickly. In March, Shingrix had already hit the shelves at most CVS, Walgreens and Duane Reade stores across the U.S. 

“Our focus is now getting all of the ducks in a row so that when a patient walks into the pharmacy and asks for the vaccine, it’s in stock, it’s reimbursed, and the healthcare provider knows how to give it,” Luke Miels, the company’s president of global pharmaceuticals, said on a recent conference call.

The GSK shot is also believed to be more effective, though no head-to-head studies have pitted the two vaccines against each other. In phase 3, the two-dose Shingrix showed that it is 97.2% efficacious in those age 50 and older. The CDC says the one-dose Zostavax can reduce shingles risk by 51%.

If there's one problem with those numbers, it's dosing. Deutsche Bank analysts cautioned that Shingrix's two-dose schedule might ultimately hamper sales.

RELATED: Plotting a global path to blockbuster sales, GSK grabs Shingrix nods in Europe, Japan

Signs of Shingrix’s rise—and hence Zostavax’s fall—were already showing up late last year. For the fourth quarter, GSK reeled in about $30 million in Shingrix sales, while Merck's Zostavax revenue dropped 45% to $121 million.

As one of the key products CEO Emma Walmsley is counting on for revenue growth, Shingrix has been moving fast around the world, too. Globally, it was first approved in Canada and was also greenlighted in Europe and Japan on March 23.

Analysts also have high expectations for the shot. A recent report from Clarivate Analytics puts Shingrix sales at $1.37 billion by 2022, which is twice the $668 million Zostavax returned for Merck last year.