The vaccines are still providing strong protection, a year on from the initial two doses, says the scientist who developed the Oxford-AZ vaccine.
The UK’s vaccine advisory body is set to decide whether booster doses against Covid-19 are needed this autumn, BBC reported.
Prof Dame Sarah Gilbert told the BBC that offering a third booster dose to millions of people was “a complex decision”.
And she called for more vaccines to be licensed to increase supplies.
The Joint Committee on Vaccination and Immunisation (JCVI) has already said a third top-up dose should be offered to people with severely weakened immune systems, which accounts for up to half a million people in the UK.
But it has not decided if booster doses are needed to extend protection in larger numbers of people at high risk from Covid-19, including those normally eligible for a flu jab.