Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, PO Box 230-80108, Kilifi, Kenya; Infectious Diseases Epidemiology, London School of Hygiene and Tropical Medicine, WC1E 7HT London, UK.
Epidemiology and Demography Department, KEMRI-Wellcome Trust Research Programme, PO Box 230-80108, Kilifi, Kenya.
Vaccine. 2018 Dec 18;36(52):7965-7974. doi: 10.1016/j.vaccine.2018.11.005. Epub 2018 Nov 8.
The benefits of childhood vaccines are critically dependent on vaccination coverage. We used a vaccine registry (as gold standard) in Kenya to quantify errors in routine coverage methods (surveys and administrative reports), to estimate the magnitude of survivor bias, contrast coverage with timeliness and use both measures to estimate population immunity.
Vaccination records of children in the Kilifi Health and Demographic Surveillance System (KHDSS), Kenya were combined with births, deaths, migration and residence data from 2010 to 17. Using inverse survival curves, we estimated up-to-date and age-appropriate vaccination coverage, calculated mean vaccination coverage in infancy as the area under the inverse survival curves, and estimated the proportion of fully immunised children (FIC). Results were compared with published coverage estimates. Risk factors for vaccination were assessed using Cox regression models.
We analysed data for 49,090 infants and 48,025 children aged 12-23 months in 6 birth cohorts and 6 cross-sectional surveys respectively, and found 2nd year of life surveys overestimated coverage by 2% compared to birth cohorts. Compared to mean coverage in infants, static coverage at 12 months was exaggerated by 7-8% for third doses of oral polio, pentavalent (Penta3) and pneumococcal conjugate vaccines, and by 24% for the measles vaccine. Surveys and administrative coverage also underestimated the proportion of the fully immunised child by 10-14%. For BCG, Penta3 and measles, timeliness was 23-44% higher in children born in a health facility but 20-37% lower in those who first attended during vaccine stock outs.
Standard coverage surveys in 12-23 month old children overestimate protection by ignoring timeliness, and survivor and recall biases. Where delayed vaccination is common, up-to-date coverage will give biased estimates of population immunity. Surveys and administrative methods also underestimate FIC prevalence. Better measurement of coverage and more sophisticated analyses are required to control vaccine preventable diseases.
儿童疫苗的益处严重依赖于疫苗接种覆盖率。我们在肯尼亚使用疫苗登记处（作为金标准）来量化常规覆盖率方法（调查和行政报告）中的错误，估计幸存者偏差的程度，对比及时性和使用这两种方法来估计人群免疫力。
肯尼亚基利菲健康和人口监测系统（KHDSS）中儿童的疫苗接种记录与 2010 年至 2017 年的出生、死亡、迁移和居住数据相结合。我们使用逆生存曲线来估计最新和适龄的疫苗接种覆盖率，计算婴儿期疫苗接种覆盖率的平均值，即逆生存曲线下的面积，并估计完全免疫儿童（FIC）的比例。结果与已发表的覆盖率估计值进行了比较。使用 Cox 回归模型评估了疫苗接种的风险因素。
我们分析了 6 个出生队列和 6 个横断面调查中分别为 49090 名婴儿和 48025 名 12-23 个月大的儿童的数据，发现与出生队列相比，第二年的调查高估了覆盖率 2%。与婴儿期的平均覆盖率相比，第三剂口服脊髓灰质炎、五联疫苗（Penta3）和肺炎球菌结合疫苗的静态覆盖率高估了 7-8%，麻疹疫苗的覆盖率高估了 24%。调查和行政覆盖率也低估了完全免疫儿童的比例 10-14%。对于卡介苗、Penta3 和麻疹，在医疗保健机构出生的儿童中，及时性高 23-44%，而在疫苗缺货期间首次就诊的儿童中，及时性低 20-37%。
在 12-23 个月大的儿童中进行标准的覆盖率调查会忽略及时性、幸存者和回忆偏差，从而高估保护作用。在延迟接种较为普遍的情况下，最新的覆盖率将对人群免疫力产生有偏差的估计。调查和行政方法也低估了 FIC 的流行率。需要更精确的测量覆盖率和更复杂的分析来控制疫苗可预防的疾病。
