Abstract
Epidemic surveillance is a fundamental part of public healthpractice. Addressing under-ascertainment of cases is relevant in most surveillance systems, especially in pandemics ofnew diseases with a large spectrum of clinical presentationsas it may influence timings of policy implementation andpublic risk perception. From this perspective, this articlepresents and discusses early evidence on under-ascertainment of COVID-19 and its motifs, options for surveillance,and reflections around their importance to tailor public health measures. In the case of COVID-19, systematically addressing and estimating under-ascertainment of cases is essential to tailor timely public health measures, and communicating these findings is of the utmost importance for policy making and public perception.