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Tuberculosis: Reported Disease Trends vs. BCG Vaccine Uptake

A recent posting in ProMED noted that rates of tuberculosis in North Korea have been increasing at an alarming rate in recent years, in spite of a parallel improvement in the uptake of BCG vaccine in that country. Indeed, one of the oldest controversies in medicine concerns the effectiveness of BCG vaccination to prevent tuberculosis. As of 2011, over 85% of countries continue to routinely vaccinate infants with BCG vaccine.

The following analysis was undertaken to collate concurrent trends in tuberculosis rates and BCG vaccine uptake among countries which employ the vaccine. Data for tuberculosis incidence were obtained from the Gideon database (www.GideonOnline.com) which is largely based on reporting from individual Health Ministry reports and publications of the World Health Organization. Disease rates per 100,000 population are automatically generated by Gideon, and all charts summarized in a related e-book. [1] Country-specific estimates of BCG coverage were obtained from a WHO website: http://apps.who.int/immunization_monitoring/en/globalsummary/timeseries/tscoveragebcg.htm , and supplemented by individual reporting data at http://www.who.int/countries/en/ .

Individual charts were generated which plot tuberculosis rates and estimates of vaccine uptake. [2] Charts were then collated into three categories:

A) Tuberculosis rates appear to diminish in parallel with high (>=85%) and / or increasing vaccine uptake (examples in graph A)

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B) tuberculosis rates appear to increase in parallel with high and / or increasing vaccine uptake (examples in graph B)

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C) no consistent similarity is apparent between trends in tuberculosis rates and vaccine uptake (examples in graph C).

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The latter graph also includes examples of countries (Latvia, Peru and India) in which vaccine update was initially associated with increasing disease rates, and subsequently decreasing rates; and others (Sri Lanka) in which these effects were reversed.

No attempt was made to further examine these data using tests of statistical significance, trend analysis, etc. In the following table, assignment of individual countries is based simply on the existence of overt visible trends between disease rates and vaccine uptake:


Data presented in the table suggest that only 62 countries (36%) which employ BCG vaccination have demonstrated decreasing tuberculosis rates in parallel with increased vaccine uptake; while, 49 countries (28%) have actually experienced increasing disease rates despite adequate vaccine usage. There is no apparent relationship between vaccination and disease rates in the remaining 63 countries (36%) . Countries in which a paradoxical increase in tuberculosis has paralleled expanded vaccine uptake are concentrated in Africa, Asia and the Near East; while countries in which increasing vaccine uptake is paralleled by decreased incidence are concentrated in North Africa, the Middle East, Western Europe, Oceania and the Americas region. These trends are depicted in the following map:


The above analysis is not intended to imply a causal relationship between tuberculosis incidence and vaccine uptake. In fact, any impact of BCG vaccination on disease incidence might only become apparent after several years, given the long “incubation period” associated with reactivation tuberculosis. Additional factors which might impact on the incidence of tuberculosis in many of these countries include AIDS, malnutrition, crowding, civil conflict, drug resistance, nature of laboratory facilities, and systems for case-finding, patient isolation and follow-up.

References:
1. Berger SA. Tuberculosis: Global Status, 2011. 568 pages, 894 graphs, 1142 references. Gideon e-books, http://www.gideononline.com/ebooks/disease/tuberculosis-global-status/
2. Gideon graph tool tutorial at http://www.GIDEONonline.com/wp/wp-content/uploads/Gideon-Graphs.pps

Posted by ProMED

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