An influenza pandemic, by definition, occurs only when the influenza virus mutates into something dangerously unfamiliar to our immune systems and yet is able to jump from person to person through a sneeze, cough or touch.

• 根据定义，全球流感的致病感冒病毒株，是人类免疫系统完全不曾接触过的危险突变种，能经由喷嚏、咳嗽或接触而在人与人之间传播。