"Sterling is benefiting mostly from the vaccine race - it's really the main differentiator," said Ned Rumpeltin, head of European currency strategy at TD Securities.
The pound was down around 0.4% against a stronger dollar at $1.3686.
Britain has injected over 12 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.
Britain, where some 9 million people have been given their first dose of a vaccine, said it expected its supply of COVID-19 shots would not be interrupted.