Abstract
BackgroundBacille Calmette-Guérin (BCG) vaccine is given to Canadian Aboriginal neonates in selected communities. Severe reactions and deaths associated with BCG have been reported among infants born with immunodeficiency syndromes. The main objective of this study was to estimate threshold values for severe combined immunodeficiency (SCID) incidence, above which BCG is associated with greater risk than benefit.MethodsA Markov model was developed to simulate the natural histories of tuberculosis (TB) and SCID in children from birth to 14 years. The annual risk of tuberculous infection (ARI) and SCID incidence were varied in analyses. The model compared a scenario of no vaccination to intervention with BCG. Appropriate variability and uncertainty analyses were conducted. Outcomes included TB incidence and quality-adjusted life years (QALYs).ResultsIn sensitivity analyses, QALYs were lower among vaccinated infants if the ARI was 0.1% and the rate of SCID was higher than 4.2 per 100,000. Assuming an ARI of 1%, this threshold increased to 41 per 100,000. In uncertainty analyses (Monte Carlo simulations) which assumed an ARI of 0.1%, QALYs were not significantly increased by BCG unless SCID incidence is 0. With this ARI, QALYs were significantly decreased among vaccinated children if SCID incidence exceeds 23 per 100,000. BCG is associated with a significant increase in QALYs if the ARI is 1%, and SCID incidence is below 5 per 100,000.ConclusionThe possibility that Canadian Aboriginal children are at increased risk for SCID has serious implications for continued BCG use in this population. In this context, enhanced TB Control – including early detection and treatment of infection – may be a safer, more effective alternative.
Highlights
Bacille Calmette-Guérin (BCG) vaccine is given to Canadian Aboriginal neonates in selected communities
Bacille Calmette-Guerin (BCG) is a live, attenuated vaccine derived from Mycobacterium bovis
The overall mean utility value for neurological sequelae following tuberculous meningitis was 0.43
Summary
Bacille Calmette-Guérin (BCG) vaccine is given to Canadian Aboriginal neonates in selected communities. Severe reactions and deaths associated with BCG have been reported among infants born with immunodeficiency syndromes. The most severe of these – and the rarest – is disseminated BCG infection. This (page number not for citation purposes). Since 1982, eight cases of disseminated BCG infection have been reported in this population [6,7,8,9] Five of these infants were diagnosed with congenital immunodeficiency disorders, including four with severe combined immunodeficiency (SCID). All of them died either from BCG infection or other complications associated with underlying disease. These events have led to a review of BCG safety issues and policy in Canada
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