The vaccine rollout complements that of the Pfizer-BioNtech shot, which was launched in the UK in December.
However, the government has pre-bought more doses of the AstraZeneca vaccine, which is cheaper and easier to produce, store and transport.
It is hoped that a speedy deployment of the vaccines can help stem the tide of Britain's rapidly rising number of coronavirus infections.
But there are questions over the pace of the rollout, with health minister Matt Hancock saying it is being limited by the supply of shots.
Hancock said on Thursday that the government is working with both Pfizer and AstraZeneca to increase supplies.
It must quickly ramp up the rate of vaccinations in order to meet an ambitious target to inoculate more than 13 million people who are elderly, vulnerable or frontline workers by mid-February.