Britons should expect to receive repeated vaccinations against Covid-19 in future to keep pace with mutations of the virus, Prime Minister Boris Johnson said on Wednesday.
As vaccines are being rushed out across the world, researchers are considering tweaks and booster shots to make them more effective against new variants, some of which appear to spread more quickly.
Among those most concerning for scientists and public health experts are the strains first found in Britain, South Africa and Brazil.
"I think we will have to get used to the idea of vaccinating and revaccinating in the autumn as we come to face these new variants," Mr Johnson told Parliament.
This week Health Secretary Matt Hancock said Britain had agreed to buy 50 million new vaccine doses specifically for new Covid-19 variants.
The head of the Oxford Vaccine Group said on Tuesday that it was not yet clear whether a new set of vaccines were needed to fight different variants of the coronavirus, but scientists were working on new ones so there was no reason for alarm.
The University of Oxford vaccine developed with British drug maker AstraZeneca appears to offer only limited protection against mild disease caused by the South African variant of Covid-19, based on early data from a trial.
But AstraZeneca said it thought its vaccine could still protect people against severe illness caused by that strain.
Britain has already delivered more than 12.6 million first doses of Covid-19 vaccines and is on track to meet a target to vaccinate everyone in the most vulnerable groups by mid-February.
The Covid-19 pandemic has killed 2.34 million people worldwide since it emerged in China in late 2019, according to a Reuters tally, with Britain among the worst hit.
