Long-term efficacy of BCG vaccine in American Indians and Alaska Natives: A 60-year follow-up study.

CONTEXT The duration of protection from tuberculosis of BCG vaccines is not known. OBJECTIVE To determine the long-term duration of protection of a BCG vaccine that was previously found to be efficacious. DESIGN Retrospective record review using Indian Health Service records, tuberculosis registries, death certificates, and supplemental interviews with trial participants. SETTING AND PARTICIPANTS Follow-up for the period 1948-1998 among American Indians and Alaska Natives who participated in a placebo-controlled BCG vaccine trial during 1935-1938 and who were still at risk of developing tuberculosis. Data from 1483 participants in the BCG vaccine group and 1309 in the placebo group were analyzed. MAIN OUTCOME MEASURES Efficacy of BCG vaccine, calculated for each 10-year interval using a Cox regression model with time-dependent variables based on tuberculosis events occurring after December 31, 1947 (end of prospective case finding). RESULTS The overall incidence of tuberculosis was 66 and 138 cases per 100 000 person-years in the BCG vaccine and placebo groups, respectively, for an estimate of vaccine efficacy of 52% (95% confidence interval, 27%-69%). Adjustments for age at vaccination, tribe, subsequent BCG vaccination, chronic medical illness, isoniazid use, and bacille Calmette-Guérin strain did not substantially affect vaccine efficacy. There was slight but not statistically significant waning of the efficacy of BCG vaccination over time, greater among men than women. CONCLUSION In this trial, BCG vaccine efficacy persisted for 50 to 60 years, suggesting that a single dose of an effective BCG vaccine can have a long duration of protection.