The protective effect of BCG against Mycobacterium ulcerans disease: a controlled trial in an endemic area of Uganda

In a BCG vaccination trial in an area of Uganda endemic for Mycobacterium ulcerans disease ("Buruli Ulcer"), 8,856 persons were examined for the disease in mid-1970 and tuberculin tested; BCG was given by intradermal injection to a random 50% of all those with negative, low or middle grade tuberculin reactions; Twelve months later the study group was re-examined for M. ulcerans lesions and, subsequently, new cases of the disease were detected, using a hospital registration system, to December 1974. One hundred and forty-nine patients with onset since July 1970 were thus ascertained and BCG was found to offer an overall protection of 47% against the disease, similar to that observed in a previous smaller trial by the Uganda Buruli Group (UBG, 1969). However, the protective effect was confined to those with tuberculin reactions of less than 4 mm before vaccination and was apparent only in the first year of the study. BCG offered no additional protection to those with previous M. ulcerans disease or an existing BCG scar at entry into the trial, although both these groups appeared to be protected against the disease, the protective effects being 88% and 82% respectively. An initial tuberculin reaction of 4 mm (or greater) offered some protection against the disease (37%). Lesions developing in the vaccinated group, or in those with initial tuberculin reactions of 4 mm or more, were smaller than those in unvaccinated persons. No relationship was found between the protective effect of BCG and either the prevalence of persons with evidence of previous M. ulcerans disease in different geographical areas, or the incidence of new cases in different areas during the first year of the study. A decline in the incidence was observed over the study period. The findings are consistent with BCG producing only short-lasting protection against M. ulcerans disease. However, long-lasting protection and a delay in onset of the disease in vaccinated persons, as suggested by the UBG in 1969, cannot be excluded on the basis of the data currently available from this trial.