No new Covid-19 variants have emerged in China during the country's recent outbreak, since it ended its zero-Covid policy according to a genome analysis of 413 cases in Beijing. The analysis spans the time period when China lifted its most strict pandemic control policies.
The study, published in The Lancet, suggests that all cases in China were caused by existing strains. The two existing Omicron subvariants, BA.5.2 and BF.7, were among the most dominant strains in Beijing during 2022. These accounted for more than 90 per cent of local infections between November 14 and December 20, 2022.
Due to the characteristics of Beijing's population, and the circulation of highly transmissible Covid-19 strains, the results represent a snapshot of the pandemic in China.
What happened after China lifted its zero-Covid policy?
On December 7, 2022, China reportedly ended its zero-Covid strategy. The strict Covid-19 control policies included targeted lockdowns, mass testing and quarantine. Since these strict policies were lifted, surging case numbers have raised concerns that new variants could emerge. It has been almost three years since Covid-19 was declared a global pandemic. During these years, several variants, including Alpha, Beta, Gamma, Delta and Omicron have emerged, and have caused multiple waves of cases around the world.
How the study was conducted
The study authors routinely collected respiratory samples from imported and local Covid-19 cases in Beijing, since December 2019. For the analysis, they randomly selected samples. Before December, 2022, there had been no persistent local transmissions reported in Beijing.
The authors, as part of the latest study, analysed Covid-19 samples detected in Beijing in 2022. They generated genome sequences using rapid, large-scale sequencing technology.
The authors analysed the evolutionary history and population dynamics of the genome sequences using existing high quality Covid-19 sequences.
They included a total of 2,881 high quality sequences in the study. From these, 413 new samples were randomly selected and sequences between November 14 and December 20, 2022. Since November 14, Covid-19 infections in China started to increase sharply.
Of the 413 samples, 350 were local cases and 63 were imported. According to the study, the imported cases came from 63 countries and regions.
Findings of the study
The authors analysed the 413 new sequences, and found that they all belong to existing, known Covid-19 strains. After November 14, 2022, the dominant strain in Beijing was BF.7. This strain accounted for 75.7 per cent of local infections.
BA.5.2 Omicron subvariant accounted for 16.3 per cent of local cases.
After November 14, 2022, the populations of both BA.5.2 and BF.7 in Beijing increased. There was no substantial increase in the effective size of the BA.5.2 population between November 14 and 25, 2022. However, the population size of BA.5.2 sharply increased around November 30, 2022.
The rise in the population size of BA.5.2 coincided with an increased number of BA.5.2 infections around November 30, 2022. From November 14, 2022, the population of BF.7 increased gradually.
In a statement released by The Lancet, Professor George Gao, of the Institute of Microbiology at the Chinese Academy of Sciences, and the lead author on the paper, said given the impact that variants have had on the course of the pandemic, it was important to investigate whether any new ones emerged following the recent changes to China's Covid-19 prevention and control policies. He added that the researcher's analysis suggests two known Omicron subvariants, rather than any new variants, have chiefly been responsible for the current surge in Beijing, and likely China as a whole.
Gao also said that with ongoing large-scale circulation of Covid-19 in China, it is important that researchers continue to monitor the situation closely so that any new variants that might emerge are found as early as possible.