它们共同作用引发一种免疫反应，在第二次活动前就击退入侵的寄生虫。
Together, these trigger an immune response which can fight off invading parasites before the second act.
“这次活动主要是为了第二次未接种或接种无效果的儿童增强免疫”，他说。
"It's a catch-up campaign to boost the levels of immunity among children who may have missed the second dose, or in whom one of the doses was not effective," he said.
已经得过水痘的小孩会对它免疫，所以不会再得第二次。
Children who have gotten the chickenpox build an immunity to it so that they do not get it a second time.
已经得过水痘的小孩会对它免疫，所以不会再得第二次。
Children who have gotten the chickenpox build an immunity to it so that they do not get it a second time.
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