South African Centre for Epidemiological Modelling and Analysis (SACEMA), Stellenbosch University, Stellenbosch, South Africa.
South African Centre for Epidemiological Modelling and Analysis (SACEMA), Stellenbosch University, Stellenbosch, South Africa.
Vaccine. 2024 Oct 3;42(23):126062. doi: 10.1016/j.vaccine.2024.06.029. Epub 2024 Jul 4.
In the context of polio eradication efforts, accurate assessment of vaccination programme effectiveness is essential to public health planning and decision making. Such assessments are often based on zero-dose children, estimated using the number of children who did not receive the first dose of the Diphtheria-Tetanus-Pertussis containing vaccine as a proxy. Our study introduces a novel approach to directly estimate the number of children susceptible to poliovirus type 2 (PV2) and uses this approach to provide district-level estimates for South Africa of susceptible children born between 2017 and 2022. We used district-level data on annual doses of inactivated poliovirus vaccine (IPV) administered, live births, and population sizes, from 2017 through 2022. We imputed missing vaccination data, implemented flexible assumptions regarding dose distribution in the eligible population, and used estimated efficacy values for one, two, three, and four doses of IPV, to compute the number of susceptible and immune children by birth year. We validated our approach by comparing an intermediary output with zero-dose children (ZDC) estimated using data reported by WHO/UNICEF Estimates of National Immunization Coverage (WUENIC). Our results indicate high heterogeneity in susceptibility to PV2 across South Africa's 52 districts as of the end of 2022. In children under 5 years, PV2 susceptibility ranged from approximately 30 % in districts including Xhariep (31.9 %), Ekurhuleni (30.1 %), and Central Karoo (29.8 %), to less than 4 % in Sarah Baartman (1.9 %), Buffalo City (2.1 %), and eThekwini (3.2 %). Our susceptibility estimates were consistently higher than ZDC over the timeframe. We estimated that ZDC decreased nationally from 155,168 (152,737-158,523) in 2017 to 108,593 in 2021, and increased to 127,102 in 2022, a trend consistent with ZDC derived from data reported by WUENIC. While our approach provides a more comprehensive profile of PV2 susceptibility, our susceptibility and ZDC estimates generally agree in the ranking of districts according to risk.
在消灭脊髓灰质炎的努力中，准确评估疫苗接种计划的效果对于公共卫生规划和决策至关重要。此类评估通常基于零剂量儿童，使用未接种白喉、破伤风、百日咳含毒疫苗的儿童数量作为替代指标进行估算。我们的研究提出了一种直接估算对脊髓灰质炎病毒 2 型（PV2）易感儿童数量的新方法，并利用该方法提供南非 2017 年至 2022 年出生的易感儿童的区级估计值。我们使用了 2017 年至 2022 年期间有关灭活脊髓灰质炎病毒疫苗（IPV）接种剂量、活产和人口规模的区级数据。我们对缺失的疫苗接种数据进行了估算，对合格人群中剂量分布进行了灵活假设，并使用了 IPV 接种一剂、两剂、三剂和四剂的估计效力值，按出生年份计算了易感和免疫儿童的数量。我们通过将中间输出结果与使用世界卫生组织/联合国儿童基金会国家免疫覆盖率估计数（WUENIC）报告的数据估算的零剂量儿童（ZDC）进行比较，验证了我们的方法。我们的结果表明，截至 2022 年底，南非 52 个区对 PV2 的易感性存在高度异质性。在 5 岁以下儿童中，PV2 易感性在 Xhariep（31.9%）、Ekurhuleni（30.1%）和 Central Karoo（29.8%）等区的范围约为 30%，而在 Sarah Baartman（1.9%）、Buffalo City（2.1%）和 eThekwini（3.2%）等区的范围不到 4%。在整个时间段内，我们的易感性估计值始终高于 ZDC。我们估计，全国 ZDC 从 2017 年的 155168（152737-158523）减少到 2021 年的 108593，2022 年增加到 127102，这与 WUENIC 报告的数据得出的 ZDC 趋势一致。虽然我们的方法提供了对 PV2 易感性的更全面描述，但我们的易感性和 ZDC 估计值在根据风险对区进行排名时大致一致。
