Evaluation of immunization coverage by lot quality assurance sampling compared with 30-cluster sampling in a primary health centre in India

Abstract

The immunization coverage of infants, children and women residing in a primary health centre (PHC) area in Rajasthan was evaluated both by lot quality assurance sampling (LQAS) and by the 30-cluster sampling method recommended by WHO's Expanded Programme on Immunization (EPI). The LQAS survey was used to classify 27 mutually exclusive subunits of the population, defined as residents in health subcentre areas, on the basis of acceptable or unacceptable levels of immunization coverage among infants and their mothers. The LQAS results from the 27 subcentres were also combined to obtain an overall estimate of coverage for the entire population of the primary health centre, and these results were compared with the EPI cluster survey results. The LQAS survey did not identify any subcentre with a level of immunization among infants high enough to be classified as acceptable; only three subcentres were classified as having acceptable levels of tetanus toxoid (TT) coverage among women. The estimated overall coverage in the PHC population from the combined LQAS results showed that a quarter of the infants were immunized appropriately for their ages and that 46% of their mothers had been adequately immunized with TT. Although the age groups and the periods of time during which the children were immunized differed for the LQAS and EPI survey populations, the characteristics of the mothers were largely similar. About 57% (95% CI, 46-67) of them were found to be fully immunized with TT by 30-cluster sampling, compared with 46% (95% CI, 41-51) by stratified random sampling. The difference was not statistically significant. The field work to collect LQAS data took about three times longer, and cost 60% more than the EPI survey. The apparently homogeneous and low level of immunization coverage in the 27 subcentres makes this an impractical situation in which to apply LQAS, and the results obtained were therefore not particularly useful. However, if LQAS had been applied by local staff in an area with overall high coverage and population subunits with heterogeneous coverage, the method would have been less costly and should have produced useful results.

PIP: During September 22-November 13, 1992 in India, staff at the National Institute of Communicable Diseases used lot quality assurance sampling (LQAS) and the 30-cluster sampling method recommended by the World Health Organization's Expanded Programme on Immunization (EPI) to evaluate immunization coverage of infants and women living in Malakhera primary health center (PHC) area in Alwar district, Rajasthan. Researchers used the LQAS survey to classify 27 mutually exclusive subunits of the population (i.e., residents in health subcenter areas) as having acceptable or unacceptable levels of immunization coverage among infants and their mothers. They combined the findings from the LQAS survey from each of the 27 subcenters to arrive at an overall estimate of immunization coverage for the entire population of the PHC: infants of all age groups, 27.7%; mothers, 46.1%. 24.1% of 11-month-old infants were immunized appropriately for their age. The LQAS survey found no subcenter to have an acceptable level of immunization coverage among infants. It identified only 3 subcenters to have an acceptable level of coverage among mothers. The researchers compared the LQAS results with those of the EPI cluster survey. According to the EPI cluster survey, immunization coverage among mothers was 56.7%, which was not significantly different from that of the LQAS survey (46.1%). Data collection took longer to complete in the LQAS survey than the EPI cluster survey (6 vs. 2 hours). Likewise, travel time was longer for the LQAS survey (90 vs. 60 minutes). The estimated cost of the LQAS survey was 60% higher than that for the EPI cluster survey (US $595 vs. $375). The homogeneous and low level of immunization coverage in the 27 subcenters resulted in an impractical situation for routine monitoring of immunization coverage using LQAS survey. It may be useful for routine monitoring of immunization programs in small areas where local staff is used and high heterogeneous coverage exists, however.