a, Expected clinical case attack rate (mean and 95% HDI) and peak in clinical case incidence for 146 countries in the Global Burden of Disease (GBD) country groupings50 for an unmitigated epidemic. b, Expected subclinical case attack rate and peak in subclinical cases. c, Estimated basic reproduction number (R0) in the capital city of each country assuming the age-specific clinical fraction shown in Fig. 2b and 50% infectiousness of subclinically infected people. d, Proportion of clinical cases in each age group at times relative to the peak of the epidemic. The 146 city epidemics were aligned at the peak, and colors mark the GBD groupings in a. e, Age distribution of the first and last thirds of clinical cases for 146 countries in GBD country groupings.