The 1918 pandemic was triggered by a bird irus that mutated into one that could attack humans, going on to kill a staggering 50 million people worldwide in a matter of months.

• 1918年的广泛流行是由一个突变为可攻击人类的禽流感引起，此病毒在世界范围内几个月内持续导致5000万人死亡。