No new Covid-19 variants have emerged in China during the recent surge in infections since the country ended its zero-Covid policy, according to an analysis of cases in Beijing published in The Lancet.

The study suggests two existing Omicron sub-variants, BA.5.2 and BF.7, among the most dominant variants in Beijing during 2022, accounted for more than 90 percent of local infections between November 14 and December 20, 2022.

Imported cases during the same period mostly involved different variants to those dominant in Beijing.

Genome analysis of 413 new Covid-19 infections in Beijing spanning the time period when China lifted its most strict pandemic control policies suggests that all were caused by existing strains.

“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. However, with an 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,” said Professor George Gao of the Institute of Microbiology at the Chinese Academy of Sciences.

The results represent a snapshot of the pandemic in China, due to the characteristics of Beijing’s population and the circulation of highly transmissible Covid-19 strains there.

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In the three years since Covid-19 was declared a global pandemic, the emergence of variants such as Alpha, Beta, Gamma, Delta, and Omicron has caused multiple waves of cases around the world.

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In the latest study, the authors analyzed Covid-19 samples detected in Beijing in 2022. Genome sequences were generated using rapid, large-scale sequencing technology, and their evolutionary history and population dynamics analyzed using existing high-quality Covid-19 sequences.

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 BF.7, which accounted for 75.7 percent of local infections. Another Omicron sub-variant, BA5.2, was responsible for 16.3 percent of local cases.

Professor Wolfgang Preiser and Dr. Tongai Maponga of the University of Stellenbosch, South Africa, who were not involved in the study, said: “It is welcome to see this much-needed data from China. It is certainly reassuring that this study yielded no evidence for novel variants but not a surprise: the surge is amply explained by the abrupt cessation of effective control measures.”

However, they urge caution in drawing conclusions about China as a whole based on data from Beijing, saying that “the SARS-CoV-2 molecular epidemiological profile in one region of a vast and densely populated country cannot be extrapolated to the entire country”.