Kolkata, Dec 30 (PTI) West Bengal has reported its first case of a mutant coronavirus strain that surfaced in the United Kingdom, a senior health official said on Wednesday.

The patient, the son of a senior official of the Calcutta Medical College and Hospital, tested positive for the mutant strain VUI-202012/01 after returning from London, the official said.

"The youth is undergoing treatment at the state-run hospital's super-specialty section. He is under observation.

We have advised all those who have come in contact with him to isolate themselves," the official told PTI, adding that the new strain is believed to be significantly more transmissible.

The youth had tested positive for COVID-19 at the Netaji Subhas Chandra Bose International Airport upon his return to Kolkata 10 days ago, he said.

"Six others who had come in contact with the youth at the airport tested negative for the infection. As he had returned from the UK, we had sent his samples for genetic analysis as per the protocol set by the Centre.

"The new strain of the coronavirus was detected during his genetic analysis. We have sent the report to Delhi-based National Centre for Disease Control," the official said.

Twenty cases of the mutant coronavirus strain have so far been reported across the country, of which eight were detected in Delhi and seven in Bengaluru.

The mutant strain VUI-202012/01 (the first Variant Under Investigation in December 2020) is defined by a set of 17 changes or mutations.

More than 40 countries including India have banned travel to and from the UK, a move several scientists said was necessary in view of the rapid spread of the VUI-202012/0, which was first detected on September 21.