South Korea's health authorities warned Saturday that their efforts to contain COVID-19 face a potentially major challenge from the spread of new variants.

Kwon Joon-wook, deputy director of the Central Disease Control Headquarters, even raised the possibility that the nation will be drawn back into a "nightmare" similar to that in December last year, when the daily number of infections exceeded 1,000.

"Mutant viruses are more contagious than existing ones," he said during a press briefing.

While the reproduction rate of the coronavirus here stands at around 0.82, it would go up to 1.2 if the mutant virus from Britain spreads widely, he added. The rate measures the number of people that the average patient infects.

It represents a very alarming situation, especially as the British government's latest announcement has signaled the odds of a higher fatality rate, Kwon added.

South Korea has confirmed three types of coronavirus variants on its soil, one each from Britain, South Africa and Brazil, with a total of 18 people infected.

On top of strict social distancing restrictions, the government is pinning hopes on a national vaccination program scheduled to begin in February.

The authorities plan to announce a specific timetable on vaccine shots next Thursday, according to another senior health official, Koh Jae-young.

South Korea has secured vaccines for 56 million people under the COVAX Facility project and separate contracts with foreign drug firms. (Yonhap)