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Analysing Covid-19 Epidemic Trajectories: are Countries Flattening the Curve?

Arnout JW Everts, Devaraj M Navaratnam, Sumitha Navaratnam, Danaraj Navaratnam

Introduction: We evaluated COVID19 epidemic trajectories of different countries in terms of relative trajectory steepness and anticipated epidemic duration, in other words “flatness of the curve”.

Methods: We used open-domain data on COVID-19 reported cases and deaths per country per day. A subset of 47 countries was analysed. Data were fitted with an analytical model following Gompertz equation. Uncertainty pertaining to the model forecasts was also quantified. To relate differences in epidemic trajectories of different countries to the mitigation approach taken by governments of those countries, we made use of the COVID-19 Government Response Stringency Index developed and published by Oxford University and Blavatnik School.

Results: Acceptable quality fits were obtained for all the countries with R2 mostly in excess of 0.98. Uncertainty on the final Cases and/or Deaths count is typically a factor of two early in the epidemic but this quickly reduces as the epidemic progresses. Uncertainty on Epidemic Duration also reduces but less fast. Statistics on key parameters like Epidemic Duration, Epidemic Peak and Final Mortality Rate were obtained and then cross-correlated with the rigor of government measures as recorded in the Stringency Score. Most significantly, we find a clear trend of decreasing Peak Epidemic height (and to a less extent, shorter Epidemic Duration) with increased Government Stringency at the epidemic onset. We also find that Final Mortality Rate decreases with increased Stringency of Government Testing and Contact-Tracing.

Conclusions: Whilst COVID-19 epidemic trajectories for most countries are similar, some countries do have flatter and less severe trajectories than others. Our analysis suggests that mitigation measures taken by a government at the very initial stage of a COVID-19 outbreak might significantly impact severity and to a less extent duration of the epidemic.