COVID-19 Transmission During the Winter 2023-24 Surge: A Comparative Analysis of Surveillance Estimates in the U.S., Canada, and the U.K.

Background: Better estimates of COVID-19 transmission are needed since testing has declined. The present investigation examined the correspondence among estimates of COVID-19 transmission during the winter 2023-24 surge using wastewater-derived estimates for the U.S. and Canada and testing-derived estimate in the U.K. to evaluate validity and provide vital public health data on transmission levels. Methods: The study used data from wastewater-derived estimates of COVID-19 transmission in the U.S. (Pandemic Mitigation Collaborative dashboard) and Canada (COVID-19 Resources Canada dashboard) and testing-based surveillance in the U.K. (Health Security Agency). Data sets were linked by date and relative to the peak transmission date within each data set. Analyses focused on the UKHSA study period of November 2023 to March 2024. Analyses 1) described transmission on the peak day, 2) examined relative agreement in the patterns of transmission via correlations, 3) examined absolute agreement on the proportion of the population actively infectious across the two months of peak transmission, and 4) described estimates of the proportion of populations infected during the peak two months. Results: On the peak day of infections, an estimated 1.95 million people were infected in the U.S., 148 thousand in Canada, and 431 thousand in the U.K., meaning an estimated 2.5%-4.5% of these populations were actively infectious. Estimates showed high relative agreement in the patterns of transmission throughout the wave, especially between the U.S. and U.K. (r=.974, p<.001). During the wave, 93.5% of U.S. estimates and 68.8% of Canada estimates had excellent or better agreement with the U.K. data. An estimated >100 million people were infected in the U.S., Canada, and the U.K. during the two peak months, or 20.9%-26.0% of each population. Discussion: Findings support the ongoing public health significance of COVID-19 by documenting high levels of transmission during the winter 2023-24 surge. Transmission estimates had high agreement across methodologies and nations. More resources are needed to prevent transmission and diagnose and treat long-term health sequelae.