Improving Outbreak Forecasts Through Model Augmentation

Abstract: Accurate forecasts of disease outbreaks are critical for effective public health responses, management of healthcare surge capacity, and communication of public risk. There are a growing number of powerful forecasting methods that fall into two broad categories -- empirical models that extrapolate from historical data, and mechanistic models based on fixed epidemiological assumptions. However, these methods often underperform precisely when reliable predictions are most urgently needed -- during periods of rapid epidemic escalation. Here, we introduce epimodulation, a hybrid approach that integrates fundamental epidemiological principles into existing predictive models to enhance forecasting accuracy, especially around epidemic peaks. When applied to simple empirical forecasting methods (ARIMA, Holt--Winters, and spline models), epimodulation improved overall prediction accuracy by an average of 9.1\% (range: 8.2--12.5\%) for COVID-19 hospital admissions and by 19.5\% (range: 17.6--23.2\%) for influenza hospital admissions; accuracy during epidemic peaks improved even further, by an average of 20.7\% and 25.4\%, respectively. Epimodulation also substantially enhanced the performance of complex forecasting methods, including the COVID-19 Forecast Hub ensemble model, demonstrating its broad utility in improving forecast reliability at critical moments in disease outbreaks.