【摘要】 １９９３年以来，我国在冬春季连续开展了４次８轮的全国强化免疫活动，据可供分析数据统计，全国４岁以下儿童累积接种５２亿人次，有效地提高了人群免疫水平。我国第４次局部范围的强化免疫活动（ＳＮＩＤｓ）分别有２６８２（第１轮）和２６５９（第２轮）个县（区、市、旗，下同）开展了强化免疫活动，分别占全国县数的９４５％和９３７％。据部分开展全省范围强化免疫省份的免疫儿童队列分析，每年强化免疫均有一定比例的漏种儿童，各出生队列的漏种率随年龄的增加而减少，同一出生队列脱漏率随经历强化免疫次数的增加而下降。因此，持续开展强化免疫活动可不断提高漏种儿童的免疫机会，降低脱漏率。更多还原

【Abstract】 Since 1993,China has conducted 4 times and 8 rounds of National lmmunization Days Activities (NIDs) in winter and spring seasonsAccording to the database reported, the total number of OPV given for children under 4 years old have been at least 520 million, so the high coverage have been achieved effectively There were 2,682 (945%) counties (District, City, Banner,the same below) in the lst round and 2,659 counties (937%) in the 2nd round having conducted SNIDs in 1996/1997 The number of immunized children under 4 years old decreased about 113% and 122% if comparing with 3rd NIDsBased on birth_cohort analysis of 10 provinces at high risk,a certain proportion of children there had been missed by each NIDs, and the proportion of children being missed decreased as the age of children increased For children from same cohort, the more NIDs conducted the more children missed will bereached by chance,so maintaining the NIDs activities can reduce the drop out rate更多还原