Epidemiology and Infection


Clustered lot quality assurance sampling: a tool to monitor immunization coverage rapidly during a national yellow fever and polio vaccination campaign in Cameroon, May 2009

L. PEZZOLIa1 c1, R. TCHIOa2, A. D. DZOSSAa3, S. NDJOMOa3, A. TAKEUa3, B. ANYAa4, J. TICHAa4, O. RONVEAUXa5 and R. F. LEWISa6

a1 World Health Organization, Geneva, Switzerland

a2 Expanded Programme for Immunization, Ministry of Health, Yaoundé, Cameroon

a3 National Institute of Statistics, Yaoundé, Cameroon

a4 Immunization, World Health Organization, Yaoundé, Cameroon

a5 Immunization and Vaccine Development, World Health Organization, Ouagadougou, Burkina Faso

a6 Epidemic Readiness and Intervention, World Health Organization, Geneva, Switzerland


We used the clustered lot quality assurance sampling (clustered-LQAS) technique to identify districts with low immunization coverage and guide mop-up actions during the last 4 days of a combined oral polio vaccine (OPV) and yellow fever (YF) vaccination campaign conducted in Cameroon in May 2009. We monitored 17 pre-selected districts at risk for low coverage. We designed LQAS plans to reject districts with YF vaccination coverage <90% and with OPV coverage <95%. In each lot the sample size was 50 (five clusters of 10) with decision values of 3 for assessing OPV and 7 for YF coverage. We ‘rejected’ 10 districts for low YF coverage and 14 for low OPV coverage. Hence we recommended a 2-day extension of the campaign. Clustered-LQAS proved to be useful in guiding the campaign vaccination strategy before the completion of the operations.

(Accepted February 13 2011)

(Online publication March 22 2011)


c1 Author for correspondence: Dr L. Pezzoli, Epidemiology Consultant, World Health Organization, Geneva, Switzerland. (Email: Lorenzo.pezz@gmail.com)