Covid-19: Keeping a close eye on the models

Since the start of the pandemic, mathematical models have been used to provide evidence-based short-term forecasts of Covid-19 cases and deaths that have helped public health decision-making. The European Covid-19 Forecast Hub, coordinated by the European Centre for Disease Prevention and Control (ECDC), is bringing together infectious disease modellers from around the world and collating their models to create the best possible forecasts.

Helen Johnson, mathematical modeller at the ECDC in Sweden: “To look at any one model is always somewhat limited. A really good approach is to combine multiple models together. This is often done in climate modelling.” – Read the full interview of Helen Johnson

30 modelling teams

Each week, around 30 modelling teams submit their forecasts for the number of Covid-19 cases and deaths over the coming four weeks for up to 30 EU/EEA Member States, the UK and Switzerland.

Combining their work in a single ‘ensemble forecast’ reduces the variance of predictions (which make assumptions about factors such as testing rates and vaccine uptake) and results in a forecast that is consistently more accurate than almost all the individual contributions.

The benefit of joint forecasting has also been demonstrated in climate forecasting and by the US CDC (Centers for Disease Control and Prevention) when predicting outbreaks of seasonal influenza.

Many of the teams that are contributing to the European forecast hub are informing policy makers in their own countries and the forecasts are publicly available and monitored by the European Commission. The press is also contributing to increase the visibility of the forecasts. One of the strengths of the European forecast hub is that it is building a network of infectious disease modellers across Europe that are able to inform decision-makers.

Helen Johnson: “It takes time for people to become comfortable and confident with what modelling can and can’t do. In the last year, many Member States have increased the extent to which they conduct, think about and call upon modelling.”

Evolution to long-term scenarios

Both Johnson and Elizabeth Lee, an epidemiologist specialising in infectious diseases at the Johns Hopkins Bloomberg School of Public Health in the US, agree that current models for short-term forecasting are pretty good at predicting what is going to happen in the next few weeks. Over the course of the pandemic, Lee’s work has evolved to making longer-term projections.

Elizabeth Lee, epidemiologist specialising in infectious diseases at the Johns Hopkins Bloomberg School of Public Health in the US: “When we try to look further into the future, I would not say it is a forecast anymore but rather a ‘scenario’ that makes assumptions about relatively realistic possibilities, so decision-makers can plan and compare the potential impact of specific interventions.” – Read the full interview of Elizabeth Lee

The ECDC is also conducting scenario- or ‘what-if’ modelling to guide planning and policy.

Disease forecasting in the spotlight

Covid-19 has put disease modellers in the spotlight and highlighted the value of mathematical modelling for public health. Initiatives such the European Covid-19 Forecast Hub and projects such as the CoMix study funded by the European Union, which is surveying thousands of people about their awareness, attitudes and behaviours in response to Covid-19 over the course of the pandemic, are helping to improve modelling not just for Covid-19 but for other infectious diseases as well.

Elizabeth Lee: “It will be really interesting to look back and see how different types of models have performed over time. We may find that models with certain features performed better at certain points in the pandemic. We will be able to tweak them to perform better for future outbreaks of Covid-19 or other infectious diseases.”

Forecasting efforts will soon be going global as the World Health Organization recently announced that it will establish a hub for Pandemic and Epidemic Intelligence based in Germany to monitor emerging pandemic threats worldwide. The new hub will further boost cooperation between countries and scientific institutes.