By Ben Hirschler
LONDON (Reuters) - GlaxoSmithKline's new shingles vaccine - a priority product as the company strives to improve its drugs line-up - has won more than 90 percent U.S. market share just five months after its launch, prescription-tracking data show.
The healthy take-up comes at the expense of Merck & Co's older and less effective product Zostavax, which has seen a slump in demand.
The U.S. Centers for Disease Control and Prevention has recommended Shingrix over Zostavax in adults 50 years and older, spurring demand for the GSK vaccine.
Deutsche Bank analysts said on Tuesday the prescription data to mid-March implied "a very strong launch", even though the figures compiled by health information company IQVIA capture only 50 to 60 percent of the market.
A GSK spokesman declined to comment on the Shingrix launch ahead of the company's first-quarter results on April 25, when sales of the vaccine are likely to be a focus for investors.
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Current consensus market forecasts point to Shingrix sales of less than 200 million pounds ($280 million) this year, which may prove to be an underestimate in the light of the positive market reception.
Zostavax's worldwide sales were $668 million last year and analysts are betting GSK can better that, with consensus for 2024 of $1.8 billion, according to Thomson Reuters data.
Adding to U.S. sales momentum is the fact that Shingrix can now be obtained at thousands of pharmacies, with CVS Health last month offering it at all its locations and Walgreens Boots Alliance making it available at most Walgreens and Duane Reade stores.
GSK has high hopes for Shingrix, which it expects to become its biggest single vaccine over time. The more than 100 million adults eligible for vaccination in the United States represent a key opportunity.
Chief Executive Emma Walmsley and her pharmaceuticals head Luke Miels have made sales of Shingrix in major markets a top priority as the British drugmaker adopts a more focused commercial approach.
The shingles vaccine was also approved in Europe and Japan on March 23.
Shingrix is given in two doses, separated by two to six months, while Zostavax is a single shot. Ensuring patients adhere to the two-shot regimen will be important in achieving the vaccine's full sales potential.
Shingles is caused by reactivation of the varicella zoster virus that is also responsible for chickenpox. Nearly all adults over 50 have the virus dormant in their nervous system and are at risk of it being reactivated with advancing age.
($1 = 0.7062 pounds)
(Editing by Alexandra Hudson)