Abstract
The BCG vaccine is currently the only approved tuberculosis vaccine and is widely administered worldwide, usually during infancy. Previous studies found increased rates of lymphoma and leukemia in BCG-vaccinated populations. To determine whether BCG vaccination was associated with cancer rates in a secondary analysis of a BCG vaccine trial. Retrospective review (60-year follow-up) of a clinical trial in which participants were assigned to the vaccine group by systematic stratification by school district, age, and sex, then randomized by alternation. The original study was conducted at 9 sites in 5 US states between December 1935 and December 1998. Participants were 2963 American Indian and Alaska Native schoolchildren younger than 20 years with no evidence of previous tuberculosis infection. Statistical analysis was conducted between August 2018 and July 2019. Single intradermal injection of either BCG vaccine or saline placebo. The primary outcome was diagnosis of cancer after BCG vaccination. Data on participant interval health and risk factors, including smoking, tuberculosis infection, isoniazid use, and other basic demographic information, were also collected. A total of 2963 participants, including 1540 in the BCG vaccine group and 1423 in the placebo group, remained after exclusions. Vaccination occurred at a median (interquartile range) age of 8 (5-11) years; 805 participants (52%) in the BCG group and 710 (50%) in the placebo group were female. At the time of follow-up, 97 participants (7%) in the placebo group and 106 participants (7%) in the BCG vaccine group could not be located; total mortality was 633 participants (44%) in the placebo group and 632 participants (41%) in the BCG group. The overall rate of cancer diagnosis was not significantly different in BCG vaccine vs placebo recipients (hazard ratio, 0.82; 95% CI, 0.66-1.02), including for lymphoma and leukemia. The rate of lung cancer was significantly lower in BCG vs placebo recipients (18.2 vs 45.4 cases per 100 000 person-years; hazard ratio, 0.38; 95% CI, 0.20-0.74; P = .005), controlling for sex, region, alcohol overuse, smoking, and tuberculosis. Childhood BCG vaccination was associated with a lower risk of lung cancer development in American Indian and Alaska Native populations. This finding has potentially important health implications given the high mortality rate associated with lung cancer and the availability of low-cost BCG vaccines.
Highlights
Live attenuated Mycobacterium bovis BCG vaccine was developed to prevent tuberculosis (TB), consistently a leading infectious cause of death worldwide.[1]
The rate of lung cancer was significantly lower in BCG vs placebo recipients (18.2 vs 45.4 cases per 100 000 person-years; hazard ratio, 0.38; 95% CI, 0.20-0.74; P = .005), controlling for sex, region, alcohol overuse, smoking, and tuberculosis
Childhood BCG vaccination was associated with a lower risk of lung cancer development in American Indian and Alaska Native populations
Summary
Live attenuated Mycobacterium bovis BCG vaccine was developed to prevent tuberculosis (TB), consistently a leading infectious cause of death worldwide.[1] The BCG vaccine is currently administered to infants or children in countries with high TB prevalence and is the only vaccine approved by the World Health Organization to prevent TB It is highly effective at preventing extrapulmonary disseminated TB and TB meningitis, but trials have shown inconsistent efficacy against pulmonary TB.[2] In some cases, the BCG vaccine’s protective effect against TB may persist for more than 50 years.[3] In addition to preventing TB infection, BCG is the standard of treatment care for non–muscle invasive bladder cancer and has been associated with several immunomodulatory effects.[4,5]. A systematic review[13] showed a nonsignificant reduction in childhood leukemia (summary odds ratio, 0.73; 95% CI, 0.50-1.08) among BCG vaccine recipients. Information about malignant neoplasm development was collected during a 60-year follow-up analysis of a clinical trial of BCG vaccination in American Indian and Alaska Native (AI/AN) populations
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