Figure 6. Survival of patients with smallpox from date of symptom onset. Survival stratified by vaccination status (P = 0.005) (top left); type of vaccination (global P = 0.012; P = 0.005 for successful vs. none; P = 0.034 for recent primary vs. none) (top right); disease severity (P < 0.001) (bottom left); and age (global P = 0.015; P = 0.008 for patients younger than 5 years of age vs. patients 5 years of age or older and younger than 45 years of age; P = 0.048 for patients 45 years of age or older vs. patients 5 years of age or older and younger than 45 years of age) (bottom right). Symbols indicate deaths, and the numbers of patients at risk are indicated at 7-day intervals along the x-axis.