Insights into COVID-19 Epidemiology and Control from Temporal Changes in Serial Interval Distributions in Hong Kong

The serial interval distribution is used to approximate the generation time distribution, an essential parameter to predict the effective reproductive number “ R t ”, a measure of transmissibility. However, serial interval distributions may change as an epidemic progresses rather than remaining constant. Here we show that serial intervals in Hong Kong varied over time, closely associated with the temporal variation in COVID-19 case profiles and public health and social measures that were implemented in response to surges in community transmission. Quantification of the variation over time in serial intervals led to improved estimation of R t , and provided additional insights into the impact of public health measures on transmission of infections. One-Sentence Summary Real-time estimates of serial interval distributions can improve assessment of COVID-19 transmission dynamics and control. ### Competing Interest Statement BJC consults for AstraZeneca, Fosun Pharma, GSK, Moderna, Pfizer, Roche and Sanofi Pasteur. The authors report no other potential conflicts of interest. ### Funding Statement Health and Medical Research Fund, Health Bureau, Government of the Hong Kong Special Administrative Region grant COVID190118 (BJC) and grant 20190712 (STA); Collaborative Research Scheme grant C7123-20G and grant T11-705/14N, Research Grants Council, Government of the Hong Kong Special Administrative Region (BJC); AIR@innoHK program of the Innovation and Technology Commission, Government of the Hong Kong Special Administrative Region (STA, ZD, EHYL, PW, GML, BJC); European Research Council (grant no. 804744); the Grand Challenges ICODA pilot initiative, delivered by Health Data Research UK and funded by the Bill & Melinda Gates Foundation and the Minderoo Foundation (LW); The funding bodies had no role in study design, data collection and analysis, preparation of the manuscript, or the decision to publish. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Our study received ethical approval from the Institutional Review Board of the University of Hong Kong (ref: UW 20-341). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data, code, and materials used in the analyses in main text and supplementary materials will be available together with the publication of this paper.