Towards universal childhood immunisation : An evaluation of measurement methods
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Childhood immunisation programming is an essential part of every country’s health programme to reduce vaccine preventable diseases. The Global Alliance on Vaccines and Immunisation (GAVI) was established to help fund and implement universal childhood immunisation. Funding provided by GAVI through its immunisation service support (ISS) is performance-based, with funds disbursed in proportion to the targeted or reported number of additional children immunised. In 2008, Lim, Stein, Charrow and Murray published the article “Tracking progress towards universal childhood immunisation and the impact of global initiatives: a systematic analysis of three-dose diphtheria, tetanus, and pertussis immunisation coverage“ in the Lancet. In the article, they raise a concern that fewer children have been immunised than officially reported and that this has significant health and financial consequences. The main findings from the assessment of this study are as follows: a) The study by Lim et al. (2008) estimates DTP3 coverage using officially reported coverage and survey data for 193 countries. Time-series analysis investigates the association between the presence of GAVI ISS and the difference between countries officially reported and survey based immunisation coverage. b) In general, vaccination coverage based on administrative data was significantly higher than survey based vaccination coverage estimates. Furthermore, the study showed that 7.4 million additional children were immunised under ISS based on survey data compared to 13.9 million addition children reportedly immunised. This amounts to a difference of around US$140 million in support money. c) We believe the amount of data analysed in the study is extensive and indicates that results are of a robust nature. The methodology (including the use of selfreported vaccinations) is validated with additional background information and studies supporting the authors’ decisions. d) The study shows that their new imputation method, bidirectional distancedependent regression (BDDR), performs similarly to the more commonly used multiple imputation method, validating its use. However, we believe in the absence of survey data, quick changes in immunisation coverage may not always be detected by the model, especially in recent estimates where there are no following surveys. e) The study by Lim et al. (2008) has lumped together investment and reward payments for countries receiving GAVI ISS, which we believe may be problematic due to the differing nature of payment calculations. f) Additionally, we believe vulnerable groups may be less likely to participate in surveys and similarly be difficult to reach for preventive health care programmes. This implies survey data may overestimate immunisation coverage. In order to learn more about potential disparities between vaccination coverage reported in surveys and administrative data we have carried out case studies in four countries. Despite the existence of clearly defined administrative routines, the overall impression is that administrative data are subject to considerable uncertainty. a) The countries selected for field studies all experienced high staff turnover and vacancies. There was a lack of relevant personnel and inadequate resources both in the organisations set up to give vaccines and to record the administrative data. b) A lack of understanding for the importance of accurate reporting of vaccinations was often observed. c) Measures of the target population (the number of children to be vaccinated) are often uncertain.