The decision is expected to help reduce the risk of supply constraints for effective vaccines as the government moves to ramp-up inoculations in the UK over the coming weeks.
Late-stage clinical trial results for another shot, from Johnson&Johnson subsidiary Janssen, are expected towards the end of January and may further aid vaccination efforts.
Government also announced on Friday that the UK had ordered another 10m doses from the same US biotechnology outfit, taking the total tally to 17m and with deliveries expected to start in the spring.
Prime Minister, Boris Johnson, has set out an ambitious plan to vaccinate 15m of the most vulnerable Britons by mid-February, a move which if successful should put a big dent in the number of fatalities from Covid-19.
So far, 1.5m people had received at least the first dose with a second one needed afterwards in order to provide longer-lasting protection.
That may allow for a quicker reopening of the economy as well.