Estimation of measles vaccination coverage using the Lot Quality Assurance Sampling (LQAS) method--Tamilnadu, India, 2002-2003.

INTRODUCTION

As part of the global strategic plan to reduce the number of measles deaths in India, the state of Tamilnadu aims at > or =95% measles vaccination coverage. A study was conducted to measure overall coverage levels for the Poondi Primary Health Center (PPHC), a rural health-care facility in Tiruvallur District, and to determine whether any of the PPHC's six health subcenters had coverage levels <95%.

METHODS

The Lot Quality Assurance Sampling (LQAS) method was used to identify health subcenters in the PPHC area with measles vaccination coverage levels <95% among children aged 12-23 months. Lemeshow and Taber sampling plans were used to determine that the measles vaccination status of 73 children aged 12--23 months had to be assessed in each health subcenter coverage area, with a 5% level of significance and a decision value of two. If more than two children were unvaccinated, the null hypothesis (i.e., that coverage in the health subcenter was low [<95%]) was not rejected. If the number of unvaccinated children was two or fewer, the null hypothesis was rejected, and coverage in the subcenter was considered to be good (i.e., > or =95%). All data were pooled in a stratified sample to estimate overall total coverage in the PPHC area.

RESULTS

For two (33.3%) of the six health subcenters, more than two children were unvaccinated (i.e., coverage was <95%). Combining results from all six health subcenters generated a coverage estimate of 97.7% (95% confidence interval = 95.7-98.8) on the basis of 428 (97.7%) of 438 children identified as vaccinated.

CONCLUSION

LQAS techniques proved useful in identifying small health areas with lower vaccination coverage, which helps to target interventions. Monthly review of vaccination coverage by subcenter and village is recommended to identify pockets of unvaccinated children and to maintain uniform high coverage in the PPHC area.