当1974年制定扩大免疫计划时,发展中国家很少有儿童进行免疫接种,直到疾病威胁发生才普遍给学龄儿童免度,而且疫苗本身常常效力尚不可靠。现尚未获得1974年婴儿一岁时可靠的免疫覆盖率。但根据已用疫苗的总数估计,一岁婴儿在第一年接受三次白喉一百日咳—破伤风三联疫苗或脊髓 When the expansion plan was introduced in 1974, there were very few children in developing countries who were immunized until the onset of the disease was generally free of school-age children and the efficacy of the vaccine itself was often unreliable. Reliable immunization coverage of infants at the age of one in 1974 is not yet available. However, based on the total number of vaccines used, one-year-old infants received three doses of the diphtheria-one hundred cough-tetanus triple vaccine or spinal cord in the first year