The BCG World Atlas: a database of global BCG vaccination policies and practices

25 Mar 2011

Paul Chinnock

Source: TropIKA.net

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Home page of the BCG World Atlas (http://www.bcgatlas.org/) and example of BCG policies and practices in Japan.

Nearly a century after it was first developed, the Bacille Calmette-Guérin (BCG) vaccine is still the only vaccine used to protect against tuberculosis. It is a weakened form of the organism Mycobacterium bovis, which is related to Mycobacterium tuberculosis – the cause of most cases of TB in humans. BCG’s efficacy is highly variable depending, for instance, on the location in which it is used and on the age of the individual receiving the vaccination. Different BCG substrains also induce different levels of protection.

Policies on the use of BCG vaccination vary from country to country and have changed, within countries, over the years. This situation causes problems, particularly in the case of migrants with suspected TB; doctors treating these patients generally do not know their “BCG history” – whether they have been vaccinated, at what age, and with which substrain. Diagnosing TB in such patients is especially problematic, as previous exposure to BCG affects diagnostic results. For example, the tuberculin skin test (TST), which is still the most commonly used test for TB, very often gives false-positive results when used with patients who have previously received BCG.

Migration is increasing, including movements of people from countries with a high TB burden. It has therefore become important for doctors to know, not only current BCG vaccination policies in patients’ countries of origin, but also the previous policies there and when these were changed. Such data has not been easy to come by.

Researchers in Canada have therefore created a free online database, the BCG World Atlas, where doctors and researchers can rapidly obtain the information they need

An article [1] in PLoS Medicine describes the process involved in establishing the database. The researchers contacted the authorities in 209 countries worldwide for information on BCG vaccination policies and practices. So far, 180 (86%) of the countries that were approached have supplied the requested details, which are now included in the Atlas.

Of these countries, 157 currently recommend universal BCG vaccination, while the remaining 23 have either stopped BCG vaccination (due to a reduction in TB incidence), or never recommended mass BCG immunization and instead favour selective vaccination of at-risk groups.

There is another reason that compiling the information available in the BCG World Atlas is likely to prove useful – in the search for new vaccines. At least six potential new vaccines have now completed Phase I clinical trials and three are currently in Phase II. Given that some of the new vaccines may work by complementing the immunity level provided by an earlier vaccination with BCG, it may be relevant to know what previous BCG vaccination individuals have had, how many and at what ages.

As the authors of the article say therefore say, the BCG World Atlas “is for clinicians, policymakers, and researchers and provides information that may be helpful for better interpretation of tuberculosis (TB) diagnostics as well as design of new TB vaccines”.

A podcast is also available in which one of the authors, Madhu Pai, explains the importance and utility of the Atlas.

Reference

Zwerling A, Behr MA, Verma A, Brewer TF, Menzies D, et al. (2011). The BCG World Atlas: A Database of Global BCG Vaccination Policies and Practices. PLoS Med 8(3): e1001012. Available from: http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1001012