Natural Schick conversion in children in two areas of Calcutta.
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004165:Diphtheria / Q000453:epidemiology / Q000276:immunology*; D006801:Humans; D007110:Immunity, Active; D007194:India; D007223:Infant; D012882:Skin Tests; D014505:Urban Population