Ka Chun Chong1,2, Yan Rui3, Kirran N Mohammad1, Yan Liu1, Tianyuan Zhou1, Maggie Haitian Wang1,2, Katherine Min Jia1, Hanqing He3. 1. From the School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong. 2. Clinical Trials and Biostatistics Laboratory Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen. 3. Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, Zhejiang Province, China.
Abstract
BACKGROUND: Supplementary immunization activities (SIAs) have been demonstrated being effective in reducing measles incidence within a short period of time in China, but the effects are short-lived if there is no follow-up SIA with high routine immunization coverage. OBJECTIVES: To assess the change in measles seroprevalence from 2009 to 2013 after the launch of 2 large-scale SIAs within the period. METHODS: Three population-based cross-sectional serologic surveys of measles antibodies were conducted in 2009, 2011 and 2013 in Zhejiang, a province in eastern China, with serologic samples collected from 1541, 896 and 1474 subjects, respectively. The serum levels of immunoglobulin G antibodies were measured by enzyme-linked immunosorbent assay. RESULTS: We found that the seropositivity rate among infants 0-7 months of age, a group having no vaccination benefit, was below 80% throughout the study period. In addition, the seropositivity rate among adults 30-49 years of age decreased significantly from 96.0% (95% confidence interval: 93.7%-98.3%) in 2011 to 88.5% (95% confidence interval: 84.3%-92.8%) in 2013. CONCLUSION: We showed that large-scale SIAs were effective, but their effects were not long lasting. Given the drop in seropositivity among adults, their susceptibility should be carefully monitored. While older individuals could benefit from the immunization activities, children who were too young to be vaccinated still have a weak seropositivity profile and the optimal age for the administration of the first dose of vaccine should be reconsidered.
BACKGROUND: Supplementary immunization activities (SIAs) have been demonstrated being effective in reducing measles incidence within a short period of time in China, but the effects are short-lived if there is no follow-up SIA with high routine immunization coverage. OBJECTIVES: To assess the change in measles seroprevalence from 2009 to 2013 after the launch of 2 large-scale SIAs within the period. METHODS: Three population-based cross-sectional serologic surveys of measles antibodies were conducted in 2009, 2011 and 2013 in Zhejiang, a province in eastern China, with serologic samples collected from 1541, 896 and 1474 subjects, respectively. The serum levels of immunoglobulin G antibodies were measured by enzyme-linked immunosorbent assay. RESULTS: We found that the seropositivity rate among infants 0-7 months of age, a group having no vaccination benefit, was below 80% throughout the study period. In addition, the seropositivity rate among adults 30-49 years of age decreased significantly from 96.0% (95% confidence interval: 93.7%-98.3%) in 2011 to 88.5% (95% confidence interval: 84.3%-92.8%) in 2013. CONCLUSION: We showed that large-scale SIAs were effective, but their effects were not long lasting. Given the drop in seropositivity among adults, their susceptibility should be carefully monitored. While older individuals could benefit from the immunization activities, children who were too young to be vaccinated still have a weak seropositivity profile and the optimal age for the administration of the first dose of vaccine should be reconsidered.