Every system dynamics modeller likes an output that tells a story, and when this matches closely to what’s actually happening there’s an additional sense of satisfaction, and confidence in the forecasts that the model generates. The simple blue line in the illustration below has been generated by an SD model that has been constantly refreshed for the Kent & Medway system since March last year. It is based on a standard SIR structure with stocks of Susceptible, Infected and Recovered people that flow through the system based on infection rates and the timing between infection, symptoms emerging and any subsequent needs for service interventions.
The model factors in underlying demographics, national lockdowns, Tiered restrictions, new variants, school opening and Christmas festivities followed by the new Lockdown in England that started on the 4thJanuary. And it matches the actuals! It then goes on to estimate the impact on hospital admissions, bed capacity, deaths management and discharge planning. And because it is fundamentally a population health model it is contributing to our understanding of the impact of COVID on subsequent health needs including Long-COVID and associated Mental Health challenges.
The system dynamic model’s ability to factor in the new COVID variant has been recognised as critical to understanding the Autumn and early Winter surge in cases and subsequent pressure on the health and care system. It has also been informative as to when, at what levels and under what circumstances this surge would run out of steam – the inevitable balancing loops that put the brakes on otherwise exponentially increases cause by reinforcing loops. This is illustrated in the diagram where the opportunity and ability of the virus to spread during the Autumn brings about a strong reinforcing cycle that even the November lockdown fails to do more than dent. The more strict lockdown from the 5thJanuary does turn things around, but we retain the risk of a resurgence given the remaining susceptible population despite the progress of the vaccination programme.
The success of the model in helping people to understand the impact of the new COVID variant in the Kent & Medway system has led to the underlying epidemiological outputs now being developed to inform plans for COVID-19 demand and capacity requirements in the NHS across the South East Region of England.
Peter Lacey, Director, Whole Systems Partnership