Assessing spatial transmission risk of respiratory infectious diseases across urban tiers in China: a modelling study

Description of Baidu Migration Data Baidu Migration data were obtained from the Baidu Qianxi platform (https://qianxi.baidu.com/). Data collection periods:1 January to 31 December 2021;1 March to 5 April 2022. Data description:The dataset includes two components: migration percentage and migration scale. Migration percentage (xᵢⱼ):Migration percentage represents the proportion of the outflow population from city i to city j, relative to the total outflow population of city i. Each day’s migration percentages were stored as a matrix, in which each element denotes the percentage (%) of population moving from the row city to the column city.Filename: "date/date_out.xlsx"Migration percentage data for the following dates were unavailable: 9 April 2021, 8 July 2021, 6 August 2021, 12 August 2021, and 25 August 2021. Migration scale.Migration scale reflects the total daily outflow population of each city and was saved in files named “date/date_规模.xlsx”. All city names in the Baidu Migration dataset were provided in Chinese. Description of Observed First Arrival Time In this study, we analysed three COVID-19 outbreaks originating in Shanghai, Nanjing, and Northwestern China. Criteria for identifying first confirmed cases:Cases were included if (i) health authorities explicitly designated them as outbreak-related, or (ii) epidemiological evidence, such as documented travel history, transportation records, or confirmed close-contact exposure, indicated that the infection was linked to one of the three source regions. Study periods:Shanghai (Omicron): 1 March-5 April 2022Nanjing (Delta): 20 July-5 August 2021Northwestern China (Delta): 17 October-3 November 2021 Screenshots of official websites reporting case information were provided. Detailed lists of first arrival times and corresponding URLs are included in the Supplementary Information.