Projecting COVID-19 intensive care admissions in the Netherlands for policy advice: February 2020 to January 2021

0. Introduction Model projections of COVID-19 incidence into the future help policy makers about decisions to implement or lift control measures. During 2020, policy makers in the Netherlands were informed on a weekly basis with short-term projections of COVID-19 intensive care unit (ICU) admissions. Here we present the model and the procedure by which it was updated. Methods the projections were produced using an age-structured transmission model. A consistent, incremental update procedure that integrated all new surveillance and hospital data was conducted weekly. First, up-to-date estimates for most parameter values were obtained through re-analysis of all data sources. Then, estimates were made for changes in the age-specific contact rates in response to policy changes. Finally, a piecewise constant transmission rate was estimated by fitting the model to reported daily ICU admissions, with a change point analysis guided by Akaike’s Information Criterion. Results The model and update procedure allowed us to make mostly accurate weekly projections, accounting for recent and future policy changes, and to adapt the estimated effectiveness of the policy changes based only on the natural accumulation of incoming data. Discussion The model incorporates basic epidemiological principles and most model parameters were estimated per data source. Therefore, it had potential to be adapted to a more complex epidemiological situation, as it would develop after 2020.