Fear of the new Omicron BA.2.12.1 spreading in the community is growing with the discovery of four cases involving the subvariant that are unrelated to any clusters.

This came as the Taikoo Shing McDonald's and St Catherine's International Kindergarten clusters saw three more infections among 251 new cases chalked up in the SAR yesterday. There were two deaths.

The Centre for Health Protection's principal medical and health officer, Albert Au Ka-wing, said the four cases with the L452Q mutation were detected on Wednesday and genetic sequencing was needed to see if Omicron BA.2.12.1, first detected in the US last month, was involved.

The four, three of whom are a family living in Lee Wing Building in Kowloon City, have each received three vaccine doses.

The 63-year-old mother, a cleaner at the Convention and Exhibition Centre in Wan Chai, first developed symptoms on May 21. She last worked on Monday and tested positive the same day.

She dined at the center's staff canteen from May 20 to Monday and also visited Po Lin Monastery's restaurant in Ngong Ping on May 19.

Her 73-year-old retired husband and daughter, 37, tested positive on Monday. The daughter last worked in Central on May 18.

The fourth case involved a 51-year-old woman living in Ka Sin House at Ka Keng Court, Sha Tin. She works at Immigration Tower in Wan Chai and was last there on May 20. She tested positive on Monday.

"If all four cases carry the BA.2.12.1 variant with the same genetic sequencing as the virus spreading in the Taikoo Shing McDonald's cluster, it would mean there are silent transmission chains," Au said.

But he said most BA.2.12.1 patients detected in Hong Kong do not have to be hospitalized as they only had mild symptoms.

The BA.2.12.1 cluster at TaiKoo Shing McDonald's saw a 99-year-old woman test positive. She had never been to the McDonald's branch but lives in the same building as a 76-year-old patient of the cluster.

That brings the cluster to 11 cases: nine diners, a friend of one of the diners and the 99-year-old woman.

The St Catherine's cluster saw two more pupils infected: one who last went to the Kowloon Tong school on Tuesday and the other from the morning class, where the outbreak happened, bringing the tally to nine.

The news came as University of Hong Kong microbiologist Ho Pak-leung, reminding people to get three jabs by Tuesday under the vaccine pass arrangement, said 700,000 had yet to get the booster shot. It also comes as Macau said it has no plans yet to administer fourth jabs.

Fears mount of new Omicron subvariant