Using an influenza surveillance system to estimate the number of SARS-CoV-2 infections in Beijing, China, weeks 2 to 6 2023

With COVID-19 public health control measures downgraded in China in January 2023, reported COVID- 19 case numbers may underestimate the true numbers after the SARS- CoV-2 Omicron wave. Using a multiplier model based on our influenza surveillance system, we estimated that the overall incidence of SARS-CoV-2 infections was 392/100,000 population in Beijing during the 5 weeks following policy adjustment. No notable change occurred after the Spring Festival in early February. The multiplier model provides an opportunity for assessing the actual COVID-19 situation. From early December 2022, the coronavirus disease (COVID-19) epidemic greatly impacted major cities in China, including Beijing [1], as a result of the predominant and highly transmissible severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron (Phylogenetic Assignment of Named Global Outbreak (Pango) lineage designation: B.1.1.529) subvariant BF.7 [2-4]. Following the adjustment of China's 'zero-COVID' policy, which included the termination of universal nucleic acid testing, the accurate number of SARSCoV-2 infections was challenging to determine. Here, we used the influenza-like illness (ILI) surveillance platform combined with laboratories of ILI virologic surveillance to understand the prevalence of SARS- CoV-2. We estimated the actual number of infected individuals in Beijing from the first week after the downgraded management of COVID-19 (week 2) to 2 weeks after the Spring Festival holiday (week 6) in 2023 using a multiplier model.