INH was significantly active in all groups, with 54 to 78% efficacy in adults, and was 100% effective in preventing meningitis and disseminated TB among children with primary TB. A subsequent report on the Bethel, Alaska, studies documented the long-term (at least 19 years) effectiveness of INH. A British Medical Research Council study in rural Kenya administered INH for 12 to 24 months to household contacts of active TB cases and demonstrated 64% efficacy.