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May 1, 2002

INTERNATIONAL IMMUNIZATION NEWS

"BCG-Induced Increase in Interferon-Gamma Response to Mycobacterial Antigens and Efficacy of BCG Vaccination in Malawi and the UK" Lancet (www.thelancet.com) (04/20/02) Vol. 359, No. 9315, P. 1393; Black, Gillian F.; Weir, Rosemary E.; Floyd, Sian

The effectiveness of the BCG vaccination against pulmonary tuberculosis can vary considerably between different populations, even when the same strain of the vaccine is used.  Previous work had found that BCG vaccination had enhanced the ability of monocytes to contain growth of Mycobacterium microti in vitro to a greater extent among people living in areas where BCG provided adequate protection against tuberculosis (TB), such as the United Kingdom, than where it did not, such as in south India. Researchers looked at two new vaccination campaigns, one involving nearly 500 adolescents and young adults in Malawi and the other with 180 adolescents in the United Kingdom, testing them for interferon-gamma response to Mycobacterium tuberculosis purified protein derivative (PPD), and for delayed type hypersensitivity (DTH) skin test response to tuberculin PPD. According to the study, the percentages of the randomized subjects who demonstrated interferon-gamma and DTH responses were higher in Malawi than in the United Kingdom pre-vaccination, with similar distributions in the two groups one year after vaccination.  In addition, although the DTH response increased after vaccination in both sites, it did to a greater extent in the United Kingdom.  The researchers note that the interferon-gamma and DTH responses were strongly linked, except among Malawi vaccinees.  In conclusion, the authors suggest that "it is likely that natural exposure and sensitization to various mycobacterial antigens gives Malawians, and people living in similar environments, some degree of natural protection against challenge with M. tuberculosis."  They also recommend further research into "the immune responses and the implications of exposure to different environmental mycobacteria in different epidemiological settings."

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