UPDATE 1-Swiss ban UK, South Africa travellers, believe mutant virus is circulating

(Adds details from news conference)

ZURICH, Dec 21 (Reuters) - Swiss officials who banned travel from Britain and South Africa on Monday on fear of mutant coronavirus variants that are spreading rapidly in those countries believe a new strain is likely already in Switzerland, despite not having detected it.

The Swiss government, among nations to levy travel restrictions, ordered people who have entered the country from the United Kingdom and South Africa since Dec. 14 to undergo a 10-day quarantine and imposed a general entry ban for foreign nationals from the countries.

The Swiss cabinet joined several countries in suspending travel for Britons after Prime Minister Boris Johnson warned the mutated variant, up to 70% more transmissible, had been identified.

Though a mutant virus has yet to be found in Switzerland, officials said travel between the two countries in recent days and weeks means such a new strain is here but has likely simply not shown up in testing or on Swiss scientists’ radar.

“The virus, unfortunately, is one step ahead of us again,” Patrick Mathys, assistant head of communicable diseases at the Federal Ministry of Health, told a news conference two days after Swiss regulators approved Pfizer and BioNTech’s vaccine against COVID-19.

Asked if Switzerland was overreacting, Mathys said there was already growing evidence that the mutant form of the virus could spread from person to person quickly, necessitating quick action to prevent an explosion of new cases.

“We know too little about the coronavirus, and we know even less about this mutant form,” he said. “But there are reliable signs emerging that it is more infectious.”

Swiss officials said there were no plans to organise evacuation charter flights for Swiss stranded abroad, and that they were considering mass testing for thousands of Britons in hotspots like Verbier, a ski area popular with British tourists.

Goods transport to and from Britain was still allowed, though the closure of the Channel Tunnel has exacerbated trade. (Reporting by Michael Shields and John Miller; Editing by Emma Farge)