A group of charities is urging the prime minister to “swiftly clarify” how many Covid vaccine doses the UK is prepared to donate to poorer countries.
Save the Children and the Wellcome Trust are among those calling on Boris Johnson to begin donating vaccines through Covax.
This scheme aims to provide jabs for low and middle-income countries.
The government said it will share “the majority of any future surplus” vaccines “when these are available”.
The UK, which has ordered 400 million vaccine doses and will have many left over, has said it will donate most of its surplus vaccine supply to poorer countries.
The lower income countries most likely to receive the first vaccines through Covax include Afghanistan, Haiti, DR Congo, Ethiopia and Somalia.