The UK government is tempering expectations, warning its people they may have to wear masks for another year, despite the country's "watershed moment" of launching its national COVID-19 vaccination program, one of the world's first. 

Britain's Government Chief Scientific Adviser(GCSA) Sir Patrick Vallance on Tuesday stressed there is a lack of evidence that the vaccines can block the spread of the virus or its propagation. He added there may be a need for face masks into the latter half of 2021, given the few months it usually takes for the vaccine to take effect. 

British Health Secretary Matt Hancock noted that the millions of people who will be given their first inoculation before Christmas won't receive their second shots until three weeks later in January.

Pledging to continue closely monitoring the virus' spread, Hancock urged people not to hamper the nation's fight against the virus.

On Tuesday, Britain's Margaret Keenan, who turns 91 next week, became the first person outside of Russia to receive a vaccine shot outside of clinical trials.