B. C. G. and vole bacillus vaccines in the prevention of tuberculosis in adolescence and early adult life. Third report to the medical research council by their tuberculosis vaccines clinical trials committee
Hart, P.D.arcy
Brit Med Jour 5336: 973-978
1963
Document Number: 499452
A controlled clinical trial of BCG and vole bacillus vaccines in the prevention of tuberculosis started in England in 1950. After exclusions, 54,239 participants were initially free both from active tuberculosis and from known contact with the disease at home. This third report presents results for aperiod of intensive follow-up until September, 1960, all the participants having by then completed between 7 1/2 and 10 years in the trial (average 8.8 years). Five-hundred and four definite cases of tuberculosis started within the period of intensive follow-up; of these 71% were of pulmonary tuberculosis and 15% of tuberculous pleural effusion without evidence of pulmonary tuberculosis. There were 2 deaths from tuberculosis in the period. For the whole period the annual incidence of tuberculosis in the BCG-vaccinated group was 0.40/ 1000, compared with 1.91/1000 among those in the tuberculin-negative unvaccinated group who were admitted concurrently; this is a reduction of 79%, attributed to vaccination. Over the same period the annual incidence of tuberculosis in the vole-bacillus-vaccinated group was 0.43/1000, compared with 2.30/1000 among those admitted concurrently to the tuberculin-negative unvaccinated group; this represents a reduction of 81%. The protective efficacy of each vaccine was thus substantial and was closely similar to that found for the shorter periods in the earlier reports. In successive 2 1/2-year periods the reductions in incidence of tuberculosis attributable to vaccination were 80%, 86%, 71%, and (provisionally) 61%. Because other factors may have been involved, this decline does not necessarily indicate that there has been any decrease in the protective efficacy of the vaccines. Whatever the reasons for the decline in the percentages, the total preventive benefit from vaccination is still substantial between 7 1/2 and 10 years. Among those with strong positive reactions to 3 tuberculin units on entry (15 mm. induration or more) the annual incidence of tuberculosis was 3.67/ 1000 in the first 2 1/2 years, very much greater than the rates in all the other groups in the same period. Subsequently, the incidence in this group became less than that in the negative unvaccinated group, and between 7 1/2 and 10 years was only slightly greater than the rates in those with initially weaker positive reactions.