幼儿百日咳发病率的下降，是与广泛使用一种适宜的免疫法直接有关。
The fall in incidence of whooping cough in the very youg is directly related to widespread immunization with suitability.
幼儿百日咳发病率的下降，是与广泛使用一种适宜的免疫法直接有关。
The fall in incidence of whooping cough in the very youg is directly related to widespread immunization with suitability.
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