Improving early epidemiological assessment of emerging Aedes-transmitted epidemics using historical data

Julien Riou; Chiara Poletto; Pierre-Yves Boëlle

Analyses conducted at the early stage of an epidemic using non-informative a priori distributions as is often done led to poor forecasts before the peak of incidence was reached, an observation already made in other studies [45] . Indeed, early forecasts of epidemic size were largely o-target and unstable, varying between 0.2 and 5.8 times the eventually observed total incidence. Worst case projections on maximal incidence were very imprecise, ranging between 2 and 63 times the eventually reached maximal weekly incidence. Using historical data led to a substantial increase of the quality of these forecasts from the very early stages of the epidemics. Using local priors, the ratio between forecasts and reality ranged between 0.4 and 1.5 for epidemic size and between 1.3 and 3.9 for maximal incidence. The less specic regional priors increased accuracy and sharpness as well, though to a lesser extent. However, the date of peak incidence and the date of the end of the period of high epidemic activity were only slightly improved by integrating historical data.