POLIOMYELITIS TRENDS IN PONDICHERRY, SOUTH-INDIA, 1989-91

Study objectives-To assess the poliomyelitis trend, including study of the epidemiological features, and to correlate this with the immunisa tion coverage of infants. Design-Three annual lameness surveys in chil dren aged 0-60 months employing cluster sampling methods and a series of five cross sectional surveys of immunisation coverage in children a ged 12-23 months of age were undertaken. Setting-Pondicherry, India, 1 988-92. Subjects-More than 10 000 children in the age group of 0-60 mo nths took part in the three annual lameness surveys and samples of 210 children aged 12-23 months were covered each year in immunisation cov erage surveys. Measurements and main results-Altogether 50 of 11 461, 24 of 10 093, and 17 of 11 218 children surveyed during 1989, 1990, an d 1991 respectively had become lame as a result of poliomyelitis, givi ng prevalences of 4.4, 2.4, and 1.5 per 1000 children for the three su rveys. The corrected prevalences of poliomyelitis were 5.9, 3.2, and 2 .0 per 1000 children during 1989, 1990, and 1991 respectively. The pro portion of cases aged up to 36 months fell from 48% in 1989 to 12.5% i n 1990 and 6% in 1991. The age at onset was less than 1 year in most. The median age at onset was 10.7 months. About 54% of the affected chi ldren had received three doses of oral poliomyelitis vaccine (OPV) bef ore the onset of paralysis. In 1988 immunisation coverage for the thir d dose of OPV was 91% and in 1992 it was 97.6%. The drop out rate for the first versus the third dose of OPV fell from 6.3% in 1988 to 1.9% in 1992. Conclusion-Three successive annual lameness surveys showed th at poliomyelitis was declining between 1989 and 1991. Five immunisatio n coverage surveys conducted from 1988 to 1992 showed high initial cov erage followed by an improvement in the form of almost universal cover age for OPV.