Temporal Evolution of COVID-19 Transmission Indicators in Tunisia During the First Three Years of the Pandemic: A Prospective Descriptive Study, 2020–2022

The first case of Coronavirus Disease 2019 (COVID-19) in Tunisia was reported on 2 March 2020. This study aimed to describe the epidemiological evolution of the COVID-19 pandemic in Tunisia from March 2020 to December 2022 and to assess changes in key transmission indicators across the different phases and epidemic waves. We conducted a nationwide longitudinal descriptive study based on prospectively collected surveillance data including all laboratory-confirmed COVID-19 cases reported through the national surveillance system between March 2020 and December 2022. Descriptive analyses were performed to estimate screening rates, test positivity rates, cumulative incidence rates, and the time-varying effective reproduction number (Rt). During the three-year study period, Tunisia reported a cumulative incidence of 9562.05 cases per 100,000 inhabitants. The mean daily screening rate was 38.23 tests per 100,000 inhabitants, while the average positivity rate reached 16.03%. The mean effective reproduction number was estimated at 1.14 (95% CI: 1.11–1.17). The epidemic evolved through two distinct transmission phases. The first phase, extending from 2 March to 17 August 2020, was characterized by limited community transmission mainly associated with imported cases. The second phase was marked by sustained autochthonous community transmission and comprised five epidemic waves. Between March and May 2021, genomic surveillance identified the predominance of the Alpha Variant of Concern (VOC). The fourth wave was dominated by the Delta VOC until December 2021, whereas the fifth wave, occurring in 2022, was associated with the Omicron VOC. Continuous monitoring of transmission indicators through the national surveillance system provided timely evidence to support risk assessment, guide public health decision-making, and adapt prevention and control measures throughout the different phases of the pandemic in Tunisia.