BEIJING – No new Covid-19 variants were detected in China during the Chinese New Year holiday when millions of people returned to their home towns, a mass migration that potentially helped the virus spread in the world’s most populous country.

The virus circulating during the holiday, which began on Jan 21, consists of older Omicron strains known as BA.5.2 and BF.7, said Chinese Centre for Disease Control and Prevention (CDC) researcher Chen Cao, at a briefing in Beijing on Monday.

There were 1,421 viral sequences submitted for analysis by various provinces across the country during the seven-day holiday, he said.

Those strains have been driving the outbreak for weeks, the Chinese CDC said.

Its surveillance published on Monday shows BF.7 accounted for 70 per cent of cases and BA.5.2 made up 28 per cent of infections between December and Jan 23, based on the sequencing of 10,165 samples.

While the testing also captured a sliver of the XBB and BQ.1 sub-variants, which have emerged as dominant strains elsewhere in the world, no others were found in China during this period.

Public health officials worldwide have been worried about new variants emerging from China as a result of the virus’ blistering spread among its 1.4 billion people.

Several countries reinstituted testing requirements for travellers coming from China after Beijing dismantled its Covid-19 restrictions in one fell swoop in early December. The move triggered a cascade of transmission that reached 80 per cent of the population in less than two months, according to Professor Wu Zunyou, the chief epidemiologist at the Chinese CDC.

The officials also said China’s outbreak has been waning since it peaked in late December, with no obvious rebound during the Chinese New Year.

The country’s hospitals saw a record 128,000 new severe patients admitted on Jan 5, with a steady decline to 36,000 on Jan 23. Covid-19-related deaths in hospitals peaked at 4,273 on Jan 4, and has since dropped nearly 80 per cent to 896 on Jan 23.

The Chinese CDC said it has consolidated data on Covid-19 infections, severe disease and deaths after local authorities stopped mandatory mass testing at the end of last year.

The information it gets is based on tests run at laboratories across the country and rapid antigen tests done at home, as well as treatment and mortality reports from hospitals. BLOOMBERG