Fatigue and adherence can challenge the prevailing wisdom on the response to severe epidemic outbreaks

After COVID-19, identifying robust epidemic control principles is a priority of preparedness. We challenge the public health wisdom that responses must be 'early, rapid and aggressive' by focusing on the roles of adherence and associated fatigue for the response's success. Using a model coupling infection transmission and human behaviour, we seek social distancing policies that optimally balance the direct epidemiological costs of an outbreak with its indirect costs. We show that adherence, fatigue and the speed at which they spread critically shape both the type (elimination, suppression and mitigation) and timing of responses depending on their interplay with policymaking priorities. Specifically, when adherence is driven solely by private perceptions, fatigue rules out elimination, limiting feasible interventions to suppression or mitigation. Suppression, prevailing at high-to-moderate health prioritization and fast individuals' responses, needs restriction-relaxation cycles to mitigate fatigue. However, different suppression regimes emerge: while high health prioritization yields overly aggressive measures exacerbating fatigue and undermining adherence, moderate prioritization achieves similar control outcomes while sustaining adherence. Additionally, slow individual responses hinder coordination between public and individual actions, compromising response effectiveness. Effective public communication then becomes essential to realign private behaviour with collective goals. Therefore, behavioural factors should be carefully considered in future response planning.