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Data On Global Vaccination Coverage Paints Overoptimistic Picture (p 1022)

September 24, 2003

Officialy reported data for vaccination coverage across the world could be misleading, conclude authors of a study in this week's issue of THE LANCET. Current methods for obtaining data in many countries is probably exaggerating the proportion of populations effectively vaccinated against common diseases.

Assessment of coverage rates in national health programmes is becoming increasingly important. Bakhuti Shengelia and colleagues from the World Health Organisation assessed the accuracy of officially reported coverage rates of vaccination with diphtheria-tetanus-pertussis vaccine (DTP3).

The investigators compared officially reported national data for DTP3 coverage with the 'gold standard' method-the household Demographic and Health Surveys (DHS) method-in 45 countries between 1990 and 2000.

Results of the study show that officially reported DTP3 coverage is higher than that reported from household surveys. For example, an officially reported coverage of 16% could be expected at a crude coverage rate of 0% from the DHS.

The investigators suggest that important reasons for differences in data quality include insufficient accounting for the vaccinations delivered outside the public sector, week health-information systems, and the presence of incentives for over-reporting.

Bakhuti Shengelia comments: "We believe that these findings have implications for efforts to gather information on the coverage of other health interventions. Worldwide, the effort to obtain valid and reliable information on vaccination coverage to support programme implementation and monitoring has been one of the most comprehensive and wide reaching in public health. However, despite impressive investment in these efforts, changes in coverage based largely on data collected from public sector service providers is not correlated with changes in coverage detected in household surveys. This absence of information on reported changes means that efforts to expand the scope of information on the coverage of health interventions must be based on careful validation studies. Coverage of health interventions is essential information for decision-makers; methods developed to monitor coverage for other interventions should be based on strategies that are likely to be valid."

Lancet