Chinese investigators said genome analysis suggests 2 existing Omicron sub-variants, BA52 and BF7, were among the most dominant variants in Beijing.
During its most severe COVID-19 resurgence in recent months, Beijing, China did not see a new COVID-19 mutation emerge. In fact, 2 existing Omicron subvariants, BA52 and BF7, accounted for more than 90% of local infections between November 14 and December 20 2022.
The results were published in The Lancet.
“Our analysis suggests two known Omicron sub-variants—rather than any new variants—have chiefly been responsible for the current surge in Beijing, and likely China as a whole,” lead author professor George Gao, of the Institute of Microbiology at the Chinese Academy of Sciences, said.
This is important as the genome analysis of 413 new COVID-19 infections in Beijing was included in the time period when China lifted its most strict pandemic control policies suggests all were caused by existing strains. The country instituted a zero-Covid strategy last year to prevent the spread of the viruse and its been reported the strategy was lifted on December 7.
The investigators generated genome sequences using rapid, large-scale sequencing technology, and their evolutionary history and population dynamics analyzed using existing high quality COVID-19 sequences.
From a total of 2881 high quality sequences included in the study, 413 new samples were randomly selected and sequenced between November 14—when infections began to increase sharply—and December 20. Of these, 350 were local cases and 63 were imported. Imported cases came from 63 countries and regions. Analysis of the 413 new sequences revealed they all belong to existing, known COVID-19 strains. The dominant strain in Beijing after November 14 2022 was BF7, which accounted for 75.7% of local infections. Another Omicron sub-variant, BA52, was responsible for 16.3% of local cases.
The investigators said that although this genome information includes only data in Beijing in November and December, they say the data is representative of the country as a whole. The number of laboratory-confirmed COVID-19 cases in December 2022 was unavailable because mandatory large-scale testing ended, suggesting the true number of infections is underestimated, leading to a degree of sampling bias in the dataset. More sampling is required to study the transmissibility and pathogenicity of Omicron sub-variants. The evolutionary rate of the virus was assumed to be constant during the initial stage of the outbreak, though it is possible this could vary depending on the variant.
“With ongoing large-scale circulation of COVID-19 in China, it is important we continue to monitor the situation closely so that any new variants that might emerge are found as early as possible,” Gao stated.