(Bloomberg) -- Roche Holding AG has run into a speed bump as it seeks to rush a pill for Covid-19 to the market: The U.K.’s aggressive vaccine drive has made it harder to find sick people to test it on.

A trial of the pill for people with mild or moderate Covid begun in the U.K. earlier this year is delayed, Roche said. To speed things up, the Swiss pharma giant has started recruiting patients in a range of other places, from Texas to Bulgaria, Canada and Spain, the U.S. clinical trials registry shows.

Roche is racing to develop a pill that patients can take at home, as are Merck & Co. and Pfizer Inc. Other effective treatments -- such as steroids, or the antibody cocktail Roche makes with U.S. biotech Regeneron Pharmaceuticals Inc. -- are either for sicker patients or, because they’re given intravenously, require a visit to a hospital or clinic.

The planning for a large late-stage trial to determine whether the pill works -- something that can’t start until the proof of concept results from the smaller study are in -- is underway, according to Chief Executive Officer Severin Schwan.

“It has become more difficult to recruit Covid-19 patients,” Schwan said in an interview with Bloomberg Television. For the final-stage trial, Schwan said “we expect results, still, by the end of this year.”

Merck, which is slightly ahead in the Covid pill development process, said last week it would focus its late-stage trial on people with milder disease after a smaller study indicated it wasn’t likely to help people who were already in the hospital.

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