A pre-registered short-term forecasting study of COVID-19 in Germany and Poland during the second wave
Authors: Bracher J. , Wolffram D. , Deuschel J. , Görgen K. , Ketterer J. L. , Ullrich A. , Abbott S. , Barbarossa M. V. , Bertsimas D. , Bhatia S. , Bodych M. , Bosse N. I. , Burgard J. P. , Castro L. , Fairchild G. , Fuhrmann J. , Funk S. , Gogolewski K. , Gu Q. , Heyder S. , Hotz T. , Kheifetz Y. , Kirsten H. , Krueger T. , Krymova E. , Li M. L. , Meinke J. H. , Michaud I. J. , Niedzielewski K. , Ożański T. , Rakowski F. , Scholz M. , Soni S. , Srivastava A. , Zieliński J. , Zou D. , Gneiting T. , Schienle M. ,   List of Contributors by Team,   CovidAnalytics-DELPHI, Li Michael Lingzhi , Bertsimas Dimitris , Bouardi Hamza Tazi , Lami Omar Skali , Soni Saksham ,   epiforecasts-EpiExpert and epiforecasts-EpiNow2, Abbott Sam , Bosse Nikos I. , Funk Sebastian ,   FIAS FZJ-Epi1Ger, Barbarossa Maria Vittoria , Fuhrmann Jan , Meinke Jan H. ,   German and Polish Forecast Hub Coordination Team, Bracher Johannes , Deuschel Jannik , Gneiting Tilmann , Görgen Konstantin , Ketterer Jakob , Schienle Melanie , Ullrich Alexander , Wolffram Daniel ,   ICM-agentModel, Górski Łukasz , Gruziel-Słomka Magdalena , Kaczorek Artur , Moszyński Antoni , Niedzielewski Karol , Nowosielski Jedrzej , Radwan Maciej , Rakowski Franciszek , Semeniuk Marcin , Zieliński Jakub , Bartczuk Rafał , Kisielewski Jan ,   Imperial-ensemble2, Bhatia Sangeeta ,   ITWW-county repro, Biecek Przemyslaw , Bezborodov Viktor , Bodych Marcin , Krueger Tyll , Burgard Jan Pablo , Heyder Stefan , Hotz Thomas ,   LANL-GrowthRate, Osthus Dave A. , Michaud Isaac J. , Castro Lauren , Fairchild Geoffrey ,   LeipzigIMISE-SECIR, Kheifetz Yuri , Kirsten Holger , Scholz Markus ,   MIMUW-StochSEIR, Gambin Anna , Gogolewski Krzysztof , Miasojedow Błażej , Szczurek Ewa , Rabczenko Daniel , Rosińska Magdalena ,   MOCOS-agent1, Bawiec Marek , Bodych Marcin , Ożański Tomasz , Pabjan Barbara , Rafajłlowicz Ewaryst , Skubalska-Rafajłowicz Ewa , Rafajłowicz Wojciech , Migalska Agata , Szczurek Ewa ,   SDSC ISG-TrendModel, Flahault Antoine , Manetti Elisa , Choirat Christine , Haro Benjamin Bejar , Krymova Ekaterina , Lee Gavin , Obozinski Guillaume , Sun Tao , Thanou Dorina ,   UCLA-SuEIR, Gu Quanquan , Xu Pan , Chen Jinghui , Wang Lingxiao , Zou Difan , Zhang Weitong ,   USC-SIkJalpha, Srivastava Ajitesh , Prasanna Viktor K. , Xu Frost Tianjian 
Published: August 2021

Disease modelling has had considerable policy impact during the ongoing COVID-19 pandemic, and it is increasingly acknowledged that combining multiple models can improve the reliability of outputs. Here we report insights from ten weeks of collaborative short-term forecasting of COVID-19 in Germany and Poland (12 October–19 December 2020). The study period covers the onset of the second wave in both countries, with tightening non-pharmaceutical interventions (NPIs) and subsequently a decay (Poland) or plateau and renewed increase (Germany) in reported cases. Thirteen independent teams provided probabilistic real-time forecasts of COVID-19 cases and deaths. These were reported for lead times of one to four weeks, with evaluation focused on one- and two-week horizons, which are less affected by changing NPIs. Heterogeneity between forecasts was considerable both in terms of point predictions and forecast spread. Ensemble forecasts showed good relative performance, in particular in terms of coverage, but did not clearly dominate single-model predictions. The study was preregistered and will be followed up in future phases of the pandemic.