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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.
The study, published in The Lancet , suggests that two existing Omicron subvariants, BA.5.2 and BF.7, among the most dominant variants in Beijing during 2022, accounted for more than 90% of local infections between November 14 and December 20, 2022.
The authors say 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.
It is widely reported that China ended its zero-Covid strategy on December 7, 2022. Since the lifting of these strict COVID-19 control policies, which included targeted lockdowns, mass testing and quarantine, the rising number of cases has raised concerns that new variants could emerge. . In the three years since COVID-19 was declared a global pandemic, the emergence of variants such as Alpha, Beta, Gamma, Delta and Omicron have caused multiple waves of cases around the world.
Since December 2019, the study authors routinely collected respiratory samples from imported and local COVID-19 cases in Beijing, and randomly selected samples for analysis. No persistent local transmissions were reported in Beijing before December 2022.
In this latest study, the authors analyzed COVID-19 samples detected in Beijing in 2022. The genome sequences were generated using large-scale rapid sequencing technology, and their evolutionary history and population dynamics were analyzed using COVID-19 sequences. existing high quality.
Of a total of 2,881 high-quality sequences included in the study, 413 new samples were randomly selected and sequenced between November 14 - when infections began to increase considerably - and December 20, 2022. Of these, 350 were cases local and 63 imported. The imported cases came from 63 countries and regions.
Analysis of the 413 new sequences revealed that they all belong to known and existing COVID-19 strains. The dominant strain in Beijing after November 14, 2022 was BF.7, which accounted for 75.7% of local infections. Another Omicron subvariant, BA5.2, was responsible for 16.3% of local cases.
The populations of BA5.2 and BF.7 in Beijing increased after November 14, 2022. The effective population size of BA.5.2 did not change substantially between November 14 and 25, 2022, but increased considerably around November 30, 2022. The increase coincided with an increased number of BA.5.2 infections around November 30, 2022. The BF.7 population gradually increased since November 14, 2022.
Lead author Professor George Gao, from the Institute of Microbiology, Chinese Academy of Sciences, said: "Given the impact variants have had on the course of the pandemic, it was important to investigate whether new ones emerged after recent changes. in China’s COVID-19 Prevention and Control Policies. Our analysis suggests that two known Omicron subvariants, rather than new variants, have been primarily responsible for the current surge in Beijing and likely in China as a whole. However, “With the continued large-scale circulation of COVID-19 in China, it is important that we continue to monitor the situation closely so that any new variants that may emerge are found as soon as possible.”
The authors acknowledge some limitations of their study. While data was only analyzed in Beijing in 2022, rather than mainland China, the authors say the data is representative of the country as a whole. The number of laboratory-confirmed COVID-19 cases in December 2022 was not available because mandatory large-scale testing ended, suggesting that the true number of infections is underestimated, leading to some degree of sampling bias in the study. data set. More sampling is required to study the transmissibility and pathogenicity of Omicron subvariants. The rate of evolution of the virus was assumed to be constant during the initial stage of the outbreak, although it is possible that this could vary depending on the variant.
Writing in a linked comment, Professor Wolfgang Preiser and Dr Tongai Matenga of Stellenbosch University, 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 turned up no evidence of new variants, but not a surprise: the increase is largely 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: “The molecular epidemiological profile of SARS-CoV-2 in one region of a vast, densely populated country cannot be extrapolated to the entire country.” . "In other regions of China, other evolutionary dynamics could develop, possibly including animal species that could become infected with humans and ’spread’ a more evolved virus."
