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预防接种对儿童常见传染病的个体保护效果目前已充分肯定,可是需要接种大部份人群,因为在理论上认为当易感人群中相当大的部分为疫苗所免疫时,余下的易感者亦会因传播环节被阻断而得到保护。这个现象称为群体免疫。评定群体免疫的成功难以在少量人群中进行
The effect of vaccination on individual protection against common infectious diseases in children is well established now but requires vaccination of the majority of the population as it is theoretically assumed that when a significant proportion of the susceptible population is immunized with the vaccine the remaining susceptible Will be blocked because of transmission links are protected. This phenomenon is called group immunity. It is difficult to assess the success of population immunization in a small number of people