Before artificial immunization，diphtheria was mainly a disease of small children.
Before artificial immunization，diphtheria was mainly a disease of small children.
在主动免疫以前，白喉是儿童的主要疾病之一。
Before artificial immunization，diphtheria was mainly a disease of small children.
在主动免疫以前，白喉是儿童的主要疾病之一。