UK PM Johnson: Vaccine programme on track but supply limits make it difficult

British Prime Minister Boris Johnson said the country's vaccine programme was on track to meet its targets, but that it would be very difficult due to supply constraints.

"I can confirm that we are on track to deliver our pledge, though it is very hard, I must stress ... it is very hard because of constraints on supply," he said, referring to a target to vaccinate the top four 'at risk' categories by mid February.