"疫情的严重性" 在英语中可以说成 "severity of the outbreak"。
"severity" 是一个形容词，意思是"严重程度"。
"outbreak" 是名词，意思是"爆发"，指的是疾病或其他类似的突发事件。
例句:
"The severity of the outbreak has prompted officials to impose strict quarantine measures." (疫情的严重性促使官员们实施严格的隔离措施。)
"Experts are closely monitoring the severity of the outbreak to determine the best course of action." (专家们正在密切监测疫情的严重性，以确定最佳行动计划。)
"The severity of the outbreak has led to a shortage of medical supppes in the affected areas." (疫情的严重性导致受影响地区医疗物资短缺。)