Evaluation of Measles Immunity among Children Aged 9 to 59 Months at Selected Health Facilities in Kwale, Narok and Lamu Counties of Kenya

Abstract

Measles burden has been on the decline globally since 1980 due to universal use of measles vaccine; with outbreaks reported in Africa, parts of Europe and Asia in 2008. Population immunity assessment is key to determining progress towards elimination of measles as advised by World Health Organisation (WHO). Kenya relies on incidence reports, since there is scanty information on prevailing measles immunity and risk awareness status. The aim of this study was to evaluate measles immunity among children aged 9 to 59 months at selected health facilities in Kwale, Narok and Lamu Counties of Kenya. This was a hospital-based cross-sectional descriptive study in which 453 children were studied. A structured questionnaire was used, blood was collected and dried blood spots (DBS) prepared. Detection of measles IgG antibodies was done by ELISA. Plaque reduction neutralization test (PRNT) was used to confirm serology equivocal results. Results were correlated with actual vaccination coverage, demographic and vaccination history data. The number and percentages of positive and negative sera were found, Chi-square used to compare proportions and a 95% confidence interval used to describe limits of percentages. Individuals found to have Measles IgG titres comparable to 200mIU/ ml, were considered protected. The study recruited 233 (51.4%) male and 220 (48.6%) female children. Most of the children 408/453 {(90.1%) 95%CI; 81.8% to 98.4%)} were vaccinated, while only 11/453 {(2.4%) 95% CI; 2.2% to 2.6%)} were not vaccinated. Among the study group, 346/453(76.4%) children had vaccination cards, 107(23.6%) did not (P < 0.001). Overall, 396/453 {(87.4%) 95% CI; 84.4% to 90.5%)} children had protective antibody titres, while 57/453 {(12.6%) 95% CI; 9.5% to 15.7%)} did not (P = 0.000). The proportion of vaccinated children with protective antibody titre was 362/408 {(88.7%) 95% CI; 85.8% to 91.6%}. The general population immunity against measles disease in the children under study was low. At 87.4%, this indicates that the herd immunity in the study group falls below the WHO recommended minimum levels of 93-95%. A country wide assessment of measles population immunity and measles vaccine awareness is required in Kenya. This shall help in identifying the most vulnerable regions and step up strategies to build up herd immunity in these zones, a good step to measles elimination in Kenya.