The Covid pandemic will "go on for a year longer than it needs to" because poorer countries are not getting the vaccines they need, the World Health Organization (WHO) says.
Dr Bruce Aylward, senior leader at the WHO, said it meant the Covid crisis could "easily drag on deep into 2022".
The UK has delivered more than 10 million vaccines to countries in need.
It has pledged a total of 100 million.
Dr Aylward appealed to wealthy countries to give up their places in the queue for vaccines in order that pharmaceutical companies can prioritise the lowest-income countries instead.
He said wealthy countries needed to "stocktake" where they were with their donation commitments made at summits such as the G7 meeting in St Ives this summer.
"I can tell you we're not on track" he said. "We really need to speed it up or you know what? This pandemic is going to go on for a year longer than it needs to."