Mapping policy and infection

New McGill project documents tuberculosis vaccination use around the world

In celebration of World Tuberculosis Day 2011, a team of researchers from the Research Institute of the McGill University Health Centre officially launched the Bacillus Calmette-Guérin (BCG) World Atlas. This website provides detailed information on current and past policies and practices for administering BCG – the only known tuberculosis (TB) vaccine – for over 180 countries.

A third of the global population has TB: the infectious disease that continues to be the number one killer in the world. It mainly affects the lungs, and symptoms include prolonged coughs, weight loss, fever, and fatigue.

Most TB infections are latent, meaning those afflicted don’t have the disease or symptoms but still test positive for the infection. In healthy, immunocompetent adults, only about 10 per cent of infected individuals will develop active TB at some point in their life. Nevertheless, the incidence of active TB surpasses 9 million every year, and ends approximately 2 million lives, according to the World Health Organization.

The most commonly used test for TB, the tuberculin skin test (TST), has been around for almost a hundred years. The test is administered by injecting a small amount of wTB antigens (substances that trigger an immune response) into the top layers of the skin and detecting whether or not a red bump forms on the site of injection, which would indicate previous exposure to TB bacteria. However, the BCG vaccination can cause false positives for this test. According to Alice Anne Zwerling, the website’s project leader and McGill PhD candidate in epidemiology, “If individuals have been vaccinated – especially if they’ve been vaccinated multiple times, or if they’ve been vaccinated later in life, after infancy, in adulthood, or as teenagers, then they’re more likely to have false positives on TST.”

Here in Canada, incoming immigrants get tuberculin skin tests as a part of routine immigrant screening. More often than not, immigrants do not remember if and when they got vaccinations. Therefore, if an individual from a foreign country tests positive for TB according to the TST, the clinician may want to know what the vaccination policy has been in the person’s country of origin in order to confirm the results. This will help in deciding whether to request further tests, which are more specific and unaffected by previous vaccinations.

Countries have different vaccination policies mostly due to the variation in level of tuberculosis incidence: smaller occurrences usually lead to a lower likelihood of BCG administration. In Canada, for example, the risk of contracting TB is very low. According to Zwerling, there are about 100 to 150 cases of active disease diagnosed every year in Montreal. On the other hand, many African nations must deal with thousands of cases every day. In this region, HIV is the single most important factor contributing to the sweeping number of TB incidences.

“TB/HIV co-infection is a huge issue,” remarked Zwerling. “If HIV-positive people are exposed to TB, they will have a much higher risk of developing TB, they are more likely to get other forms like extra-pulmonary TB – which are harder to diagnose – and they are already concerned about pneumonia and other infections.”
Furthermore, providing effective preventative treatment for all TB patients is hard in countries with high incidences that also lack the necessary tools, drugs, and infrastructure to combat the disease. Still, researchers remain optimistic about helping to cure TB patients around the world, since TB is very curable with current antibiotics. Finally, they hope the establishment of this website will be helpful for the design of new TB vaccines.

“A lot about what’s being developed now [are systems in which]…the primer is BCG, and there would [then] be a second, new vaccine,” explained Zwerling. “So in those situations they want to know which countries had [already] given BCG and which hadn’t. That would be very important information for where you do your trials.”

Although Canada does not have a high incidence of TB, McGill, along with the Public Health Agency of Canada, has taken a lead in the fight against TB by creating a free, accessible resource for clinicians, policymakers, and researchers worldwide. Perhaps this outreach to the global community can give one hope for more effective treatment of this disease in developing areas in the future.