Preventive options for tuberculosis (TB) consist of treatment of latent tuberculous infection (LTBI) or immunization with Bacille Calmette-Guèrin (BCG). BCG vaccine is an attenuated strain of Mycobacterium bovis first introduced into public health practice in the early part of the 20th century. It is the most widely administered vaccine worldwide and is routinely given in some l72 high-prevalence countries, with over 3 billion doses administered annually. Vaccine efficacy has been much discussed, and the overall protective effect has been estimated through meta-analysis at between 0 and 80%. The vaccine is likely to be most effective when infection rates are high and among children at high risk of disseminated disease. Continued high incidence rates in countries with widespread vaccine coverage suggests that BCG is a relatively poor public health measure as it does not prevent infection and its protective effect wanes with time. Further, its effect on TB skin test (TST) interpretation precludes accurate identification of infected children. In British Columbia, the only group receiving BCG vaccine was aboriginal newborns living on reserve. BCG vaccination was justified given that on-reserve aboriginals have a TB incidence rate some 10 times that of the non-aboriginal Canadian-born population. However, participation in vaccination has been variable, with declining coverage noted among eligible aboriginal communities. In recent years, only 25% of reserves actually gave the vaccination.
The continued use of BCG vaccination is currently undergoing re-evaluation in Canada, prompted largely by disturbing reports of disseminated BCG infection in children with severe congenital or acquired immunodeficiency syndromes. Widespread prenatal HIV testing should minimize the possibility of inappropriate vaccination of an HIV-infected child, but the risk to those suffering from congenital immunodeficiencies such as severe combined immunodeficiency (SCIDS) remains present. Unfortunately, in patients with SCIDS, dissemination of the BCG strain can be the first indication of an underlying problem, and several deaths have occurred in Canada. BCG vaccination does have an effect on preventing more serious forms of disease such as miliary and meningeal TB, although these have become relatively rare events in recent years.
With these concerns in mind, a review of BCG vaccination policy has been held at the national level, with widespread participation from First Nations and Inuit Health Branch (FNIHB) of Health Canada, the National Advisory Committee on Immunization (NACI), the Provincial TB Control Directors, and the National TB nursing group in collaboration with First Nation communities. Due to regional differences in the epidemiology of tuberculosis, policy changes were supported at the provincial level. The low rates of TB in the pediatric aboriginal population, the decline in vaccine acceptance, and the potential risks of vaccination presently appear to outweigh the benefits, and the FNIHB BC-Yukon Region has elected to discontinue routine BCG vaccination of on-reserve newborn aboriginal children effective 1 June 2003.
To evaluate the impact of this decision, the Division of TB Control has developed a protocol of enhanced surveillance to monitor children during this transition. All children aged 5 years or less, living in at-risk communities, will be offered enhanced surveillance. At-risk communities have been defined as those having at least one case of active TB within the last 5 years. All children born after 1 June 2003 in these communities will be offered TST at 10 months, then yearly until age 5. Positive TSTs will prompt treatment for latent TB infection using the standard 9-month isoniazid regimen. Following this cohort of children over 5 years will allow an accurate determination of the annual risk of infection. TST interpretation will be facilitated as BCG will no longer be a confounder. Enhanced screening will be discontinued should low annual risks of infection be documented. Recent low rates of BCG uptake in the province confirm that BCG has in effect already been discontinued. As of 1 June 2003 divisional policy now reflects reality. Bacille Calmette-Guèrin—adieu.
—Victoria Cook, MD, FRCPC
Director, TB Services to Aboriginals —Kevin Elwood, MB, MRCP(UK), FRCPC
Director, TB Control