No new COVID-19 variants emerged in Beijing during the surge in cases in the city late last year, according to a study published on Wednesday in the Lancet.
After operating under a zero-COVID policy for almost three years, China lifted many restrictions late last year and triggered a steep increase in cases. The seven-day rolling average of new cases per million people peaked at 29 around the start of December, raising concerns that the proliferation of the virus would lead to mutations and the emergence of new, potentially more transmissible variants of concern.
To check if that happened, researchers at the Chinese Academy of Sciences (CAS) sequenced 413 samples from November 14 to December 20. The majority – 350 – of the cases were local, as opposed to imports. All 413 samples contained existing strains of SARS-CoV-2, suggesting no new variants of concern emerged during the outbreak.
“It was important to investigate whether any new ones emerged following the recent changes to China’s COVID-19 prevention and control policies,” George Gao, a CAS professor and lead author of the paper, said in a statement. “Our 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.”
The two subvariants, BA.5.2 and BF.7, accounted for 90% of local cases. The finding is in line with the Chinese Center for Disease Control and Prevention’s report to the World Health Organization, which said that the two subvariants were responsible for 97.5% of local cases during the late-2022 surge.
Over the course of the Beijing outbreak, BA.5.2 and BF.7 became dominant and increased in genetic diversity, but the researchers found no evidence that new variants emerged in the city over those weeks. BF.7 was the dominant strain, accounting for 75.7% of the cases, followed by BA.5.2 (16.3%) and BA.5.1 (7.7%). Analysis of the imported cases revealed 16 subvariants; BQ.1 accounted for 31.8% of imports.
In an accompanying commentary, researchers from the University of Stellenbosch in South Africa list several limitations of the study, noting that the analyzed time period “was probably too early to find” new lineages, the sequenced samples represented a tiny fraction of cases, and only Beijing was included in the analysis.
“The SARS-CoV-2 molecular epidemiological profile in one region of a vast and densely populated country cannot be extrapolated to the entire country,” the researchers wrote. “In other regions of China other evolutionary dynamics might unfold, possibly including animal species that could become infected by human beings and ‘spill back’ a further evolved virus.”
Evidence of the potential for subvariants to remain confined to regions comes from the United States, where XBB.1.5 is largely restricted to northeastern parts of the country despite a mutation making it more infectious than its XBB.1 ancestor. Data up to February 4 suggest XBB.1.5 accounts for 92% of cases in the Northeast but just 30.2% of cases in the northwestern part of the country.
