Evaluating the COVID-19 responses of Belgium, Denmark, Germany, the Netherlands, Sweden and the United Kingdom, February-June 2020: A counterfactual modelling study

Introduction Differences in responses to the COVID-19 pandemic among Northwestern European countries have generated extensive discussion. We explore how the impact of the first pandemic wave might have differed, had Belgium, Denmark, Germany, the Netherlands, Sweden and the United Kingdom adopted responses from the other countries, or had it delayed its own response.

The time-varying reproduction number Rt for each country was estimated using time-series of laboratory-confirmed COVID-19 deaths. Counterfactual assessment of the impact of responses was conducted by interchanging the reduction in reproduction number by calendar date between countries from March 13th to July 1st, 2020. The impact of a delayed response was evaluated by lagging the time-series of the reproduction number with one day or three days.

The cumulative number of COVID-19 deaths for any of the six countries would have differed substantially, had the response of another country been adopted on the respective calendar date. The order, from the lowest to the highest expected mortality rate, was obtained with the responses of the Netherlands, Belgium, Denmark, the United Kingdom, Germany, and Sweden, with a seven- to twelve-fold difference between the lowest and highest outcome. For the Netherlands, delaying its response by three days resulted in a doubling of the cumulative COVID-19 mortality rate.

During the fast-growing first COVID-19 wave, small differences in initial epidemiological situations between countries, together with small differences in the timing and effectiveness of adopting COVID-19 response from neighboring countries, result in large variations in mortality rates. Competing Interest Statement The authors have declared no competing interest. Funding Statement The study was financed by the Netherlands Ministry of Health, Welfare and Sport, and the European Union's Horizon research and innovation program - project ESCAPE (grant agreement number 101095619). Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the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, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes