Short-term forecasts to inform the response to the COVID-19 epidemic in the UK

Funk, S.; Abbott, S.; Atkins, B. D.; Baguelin, M.; Baillie, J. K.; Birrell, P. J.; Blake, J.; Bosse, N. I.; Burton, J.; Carruthers, J.; Davies, N. G.; de Angelis, D.; Dyson, L.; Edmunds, W. J.; Eggo, R. M.; Ferguson, N. M.; Gaythorpe, K. A. M.; Gorsich, E.; Guyver-Fletcher, G.; Hellewell, J.; Hill, E. M.; Holmes, A.; House, T. A.; Jewell, C.; Jit, M.; Jombart, T.; Joshi, I.; Keeling, M. J.; Kendall, E.; Knock, E. S.; Kucharski, A. J.; Lythgoe, K. A.; Meakin, S. R.; Munday, J. D.; Openshaw, P. J.; Overton, C.; Pagani, F.; Pearson, J.; Perez-Guzman, P. N.; Pellis, L.; Scarabel, F.; Semple, M. G.

Background: Short-term forecasts of infectious disease can create situational awareness and inform planning for outbreak response. Here, we report on multi-model forecasts of Covid-19 in the UK that were generated at regular intervals starting at the end of March 2020, in order to monitor expected healthcare utilisation and population impacts in real time. Methods: We evaluated the performance of individual model forecasts generated between 24 March and 14 July 2020, using a variety of metrics including the weighted interval score as well as metrics that assess the calibration, sharpness, bias and absolute error of forecasts separately. We further combined the predictions from individual models to ensemble forecasts using a simple mean as well as a quantile regression average that aimed to maximise performance. We further compared model performance to a null model of no change. Results: In most cases, individual models performed better than the null model, and ensembles models were well calibrated and performed comparatively to the best individual models. The quantile regression average did not noticeably outperform the mean ensemble. Conclusions: Ensembles of multi-model forecasts can inform the policy response to the Covid-19 pandemic by assessing future resource needs and expected population impact of morbidity and mortality.