Fig. 9

Counterfactual simulations of outbreaks in Wuhan, New York, Milan and London assuming no stay-at-home and quarantine measures. Simulations were performed using posterior model parameters estimated each day in the four cities within 40 days after lockdown, with the self-isolation rate \(q_0=0\) and quarantine rates \(q_1=q_2=0\). The vertical dash lines show the starting dates of counterfactual simulations. The orange stars are the observed daily case numbers. The blue curve is the mean posterior fitting using the EAKF. Blue boxes show the median and interquartile of counterfactual simulations, and whiskers show 95% CI. The solid red lines are the median of counterfactual simulations. Counterfactual simulations were performed for 100 realizations using independently estimated model parameters