1. The BCG vaccine was found to be effective at protecting children exposed to tuberculosis (TB) from infection and progression to active disease.
2. Differences in the age of vaccination under 16 years did not affect the results.
Evidence Rating Level: 2 (Good)
Study Rundown: Clinical trials have been unable to consistently show that the BCG vaccine is protective against tuberculosis in children. Part of this difficulty has been due the limitations of the tuberculin skin test, which tests positive after exposure to Mycobacterium tuberculosis, but also tests false positive BCG vaccine administration. This study systematically reviewed the literature to find studies that used newer interferon assays to detect TB, as these tests have the ability to discriminate between exposure to TB and the BCG vaccine. The authors also selected studies that included both BCG-vaccinated and unvaccinated children under the age of 16 with known recent exposure to someone with pulmonary TB. Results revealed that compared to unvaccinated children, vaccinated children had a lower risk of tuberculosis infection. On further analysis it was found that the BCG vaccine also provides protection against progression from TB infection to active disease. Vaccination at birth versus later in childhood did not change the efficacy of the vaccine.
A key limitation of this study was incomplete availability of data, as only a few of the included studies were originally designed to study the effect of the BCG vaccine. Another limitation is that only 3 of the 14 studies the authors analyzed were considered to be of high quality on the modified Newcastle-Ottawa style. Nonetheless, this study provides evidence on the benefits of the BCG vaccine and has implications for public health in the prevention of active TB and promotion of the BCG vaccine.
In-Depth [meta-analysis]: This study systematically reviewed literature from 1950 to 2013 to find studies that included BCG-vaccinated and unvaccinated children under the age of 16 who had known exposure to TB. 14 studies (3,855 children) from around the world met the inclusion criteria for the meta-analysis which included testing with a γ interferon based testing to differentiate between vaccination and infection. The authors found that the BCG vaccine reduced the risk of TB infection, risk ratio of 0.81 (CI95%, 0.71-0.92), with a protective efficacy of 19% (i.e. 19% reduction in incidence of TB infection). This was consistent in testing with both γ interferon tests, ELISpot or QuantiFERON. Further analysis of the 6 studies (1,745 children) with data available on the progression from infection to active TB disease revealed that the BCG vaccine had a total protective efficacy of 27% against disease infection, risk ratio 0.73 (CI95%, 0.61 to 0.87), and a 58% protection (risk ratio 0.42, 0.23 to 0.77) against progression from infection to active disease. Other subgroup analysis of the effect geographical latitude and vaccination policy on infection yielded insignificant results.
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