The UK is to begin a mass-vaccination program next week after becoming the first country in the world to approve a COVID-19 vaccine developed by U.S. pharmaceutical giant Pfizer and its German partner BioNTech.

The vaccine has been described as a "game-changer" by politicians and medical professionals but UK Prime Minister Boris Johnson has urged caution, saying it's "not game over."

Bharat Pankhania, an expert in communicable disease control at the University of Exeter Medical School, told CGTN Europe: "It's important that we keep our nerve and we do this in an orderly manner."

The UK has bought 40 million doses of the jab, enough to vaccinate 20 million people. The first 800,000 doses are expected to arrive over the coming days.

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Pankhania says British authorities need to keep good records "because we also want to follow up [with] all the people that we immunize, and also survey a good representative group of people who have been immunized to look out for any unusual or unexpected side effects."

The Pfizer-BioNTech vaccine has been developed at breathtaking speed since the outbreak of the pandemic but it presents logistical challenges for doctors.

"It has to be kept at minus 70 degrees [Celcius] and once you've thawed it out, it has a lifespan of about five days, when it can be kept in a normal refrigerator at 3 to 5 degrees," Pankhania explained. 

"Secondly, you've got to administer and not waste the vaccine, because it comes in a large batch per vial of vaccine," he added.

England's deputy chief medical officer, Jonathan Van-Tam, remarked at a Downing Street press conference that the vaccine is "not a yogurt that can be taken out of the fridge and put back in multiple times, it's really tricky to handle."

Another vaccine developed by Oxford University and AstraZeneca is also expected to gain regulatory approval in the UK over the coming weeks. It uses a more traditional approach to vaccine development compared with the Pfizer-BioNTech candidate and is expected to be easier to distribute around the world.

Pankhania believes lots of rival vaccines will eventually work along with the current front-runner, which is "a good thing for humanity."