ABSTRACT
This retrospective study on COVID-19's four waves in Bogotá, Colombia, scrutinises 1.77 million cases from March 2020 to April 2022, revealing significant shifts in both transmissibility and severity. The study highlights dynamic changes in the instantaneous reproduction number (Rt), with the highest values (> 2.5) corresponding to the ancestral and Omicron variants. There was a notable 88% decrease in the Case Fatality Ratio (CFR) from the first to the fourth wave, emphasising changing severity levels. The third wave, marked by the Mu variant, saw the highest case and death counts, yet paradoxically showed a decrease in CFR and an increase in the hospitalisation fatality ratio. Conversely, the fourth wave, dominated by Omicron, had the lowest severity despite higher hospitalisation rates in children. Additionally, the study records a consistent reduction in average hospital and ICU stay durations, from 10.84 days to 7.85 days and from 16.2 days to 12.4 days respectively, across the waves. These findings underscore the importance of ongoing epidemiological surveillance and adaptable public health strategies in lower-middle-income regions like Bogotá, deepening our understanding of COVID-19's impact in Latin America.