LONDON, May 11 (Xinhua) -- A COVID-19 vaccine is "by no means guaranteed," British Prime Minister Boris Johnson said Monday night.

Speaking at a press conference, Johnson referred to the part Britain was playing in looking for a valid coronavirus vaccine.

Asked by the media, Johnson said he hopes that a vaccine will be developed, but there is no guarantee. "I'm hearing some very encouraging things from what's going on at Oxford (University) to achieve a vaccine."

"What I can tell you is that the UK is at the forefront of concerting international activity to try to deliver a vaccine," said Johnson.

The government's Chief Scientific Adviser Patrick Vallance said the chances of developing a vaccine for the disease is getting higher. But he also agreed with Johnson's comment that it was not guaranteed.

Earlier on Monday, the British government published a document of the long-expected COVID-19 recovery plan, hoping to gradually ease the lockdown measures while at the same time getting the coronavirus pandemic under control.