Peer-reviewed article
Estimation of the poliovirus type 2 immunity gap in South Africa.
Brown L, Bingham J, Pulliam J, Mthombothi Z, Sereo T et al. ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001This study develops a method to estimate how many children in South Africa are susceptible to poliovirus type 2 by analyzing vaccination data from 2017 to 2022. The researchers found large differences between districts, with some areas having up to 32% of children under 5 at risk while others had less than 4% at risk. The new approach provides more detailed information than existing methods for tracking immunization gaps and planning polio eradication efforts.
Key points
- High heterogeneity in poliovirus type 2 susceptibility across South Africa's 52 districts, ranging from 1.9% to 31.9% in children under 5
- The study's susceptibility estimates were consistently higher than estimates based on zero-dose children, suggesting the new method captures more at-risk children
- National zero-dose children estimates decreased from 155,168 in 2017 to 108,593 in 2021, then increased to 127,102 in 2022
- Districts with highest susceptibility included Xhariep (31.9%), Ekurhuleni (30.1%), and Central Karoo (29.8%)
- The novel approach ranks districts similarly to existing zero-dose child methods but provides more comprehensive susceptibility profiles
Limitations
The study relies on district-level administrative data on vaccine doses administered and may be affected by data quality issues or missing vaccination records that required imputation. The findings are specific to South Africa's context and may not generalize to other countries with different immunization programme structures.
Abstract
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.