Lot quality assurance sampling for coverage evaluation of a new vaccine: A pilot study

Worldwide, vaccine-preventable diseases have been a significant cause of mortality in the under-5 age group. To reduce the disease burden, new vaccines are being introduced in every country's immunization programmes. For this to happen, high vaccination coverage is necessary. However, rapidly identifying the areas that fail to reach the expected coverage becomes cumbersome. During recent years, lot quality assurance sampling (LQAS) has been widely used in evaluating immunization coverage across the globe. The present study aims to pilot this approach for field monitoring of a new vaccine against routine concurrent field monitoring in one of the North-Eastern states of India.

For LQAS, a community-based cross-sectional study was undertaken among 55 children aged 0-23 months in all 5 Primary health centres (lots) of Medziphema block, Dimapur, Nagaland. The total sample size for LQAS was calculated based on α = 5, β = 90 using Lemeshow and Taber-LQAS table with a target level of immunization defined as 90 % and the lower limit set to 55 %. For the concurrent field monitoring, a sample of 30 children in the same age group was selected through random sampling. Pre-designed, pre-tested questionnaire for the caregivers, scripted on a digital tool was employed with verification of immunization card and caregiver's recall. Data was analyzed using SPSS software version 25.0.

The study found a slight difference in the percentage of children age-appropriately vaccinated for PCV (as per the schedule) in concurrent field monitoring (93.3 %) and LQAS (90.9 %). However, no statistically significant difference was found in comparing the immunization coverage using both methodologies (p > 0.05).

The study findings encourage that LQAS can be considered for monitoring the immunization coverage of a newly introduced vaccine. It offers the added advantage of identifying poor/low-performing pockets that require focused attention.