Roche and Boston-based partner Atea Pharmaceuticals are hoping their AT-527 pill could offer an anti-viral therapy to treat COVID-19 patients that would be easier to administer and cheaper than other prospective treatments, such as antibody cocktails or Gilead Science's remdesivir.

In an interview in Swiss media in early March, Roche Chairman Christoph Franz had offered the tantalizing prospect of data on AT-527 "within the next weeks", saying he dreamed of being able to fight the pandemic with a pill by year's end.

But Britain's success in reducing case numbers with a swift vaccination programme and strict lockdown meant it was taking longer than expected to collect data from the trial there, said Bill Anderson, head of Roche's pharmaceutical division.

"There's just simply not enough patients to enrol...with the speed we were hoping for," Anderson said on a conference call.

"That's been one of the challenges since the beginning of the pandemic: you set up sites where there's a lot of COVID, and then by the time you're ready to enrol, the pandemic has moved somewhere else and you're sort of chasing it."

He did not identify other locations where Roche might set up trials.

Atea received an upfront payment of $350 million in cash from Roche, with potential for future milestone payments and royalties. With Roche, Atea is trialling the medicine in patients with mild to moderate COVID-19. It is also separately trialling the medicine in hospitals with patients with more severe cases.

(Reporting by John Miller; Editing by Michael Shields and Peter Graff)

By John Miller