Clotted blood samples will be centrifuged at 3000 rpm for 15 minutes to obtain serum which will be frozen at -20 degree Celsius till tested. Serum will be processed in batches of 30-40 and measles specific IgG antibodies will be quantified by micro-ELISA (enzyme linked immunosorbent assay) using commercially available quantitative measles IgG kits of high sensitivity (98-100%) and specificity (100%). IgM antibody assay will be done to confirm the diagnosis of measles only in those infants suspected to have measles; using commercially available quantitative measles IgG kits of high sensitivity (98-100%) and specificity (100%). Sera from subjects, calibrators, positive and negative controls will be diluted in serum diluents and test will be performed as recommended by the manufacturers. The obtained optical density value for each sample will be converted into measles antibody titre in units/ml with help of calibrator values in a standard log graph paper and these units/ml will then be interpreted as International Units/ml taking the recommendation in the kit.