A series of 1,716 BCG-vaccinated and 1,665 nonvaccinated infants, all born at the Cook County Hospital in Chicago between February, 1937, and February, 1948, were followed until February, 1960 (23 years). Among the vaccinated there was a total of 17 cases of tuberculosis (0.43/1,000/yr) and 65 cases in the nonvaccinated 1.7/1,000/yr), a reduction of 75%, statistically highly significant (p 0.001). The morbidity was 0.41/1,000/yr (16 cases in 1,716) in the vaccinated subjects and 1.5/1000/yr (59 cases in 1,665) in the controls, or a reduction of 74% (p 0.001). There was one death from tuberculosis in the vaccinated subjects and six in the controls, or a reduction of 83%. The number of deaths is too small for meaningful statistical analysis.
Comparisons of the control and vaccinated groups were made for subsequent contact to tuberculosis in the home and environment, sex, race, birth weight, observation years, follow-up care, general health and reasons for loss from study. The over-all comparability of the two groups was adequate in most respects. Statistically significant differences were assessed for medical importance. In 639 families in which there were both vaccinated and control siblings, 8 of the 790 vaccinated subjects developed tuberculosis as compared with 30 of the 845 control individuals. The difference is highly significant (p 0.001). Thirteen cases of nonfatal tuberculosis developed in the controls 2 years of age and under and none in the vaccinated. There were three deaths from tuberculosis in the controls under 2½ years of age (miliary tuberculosis plus meningitis in all) and one death in the vaccinated group (meningitis). The latter was an infant who had not converted at 6 months of age and was not revaccinated. Following vaccination, 99.3% became tuberculin positive and 82.4% were still positive, after 8 years, to a single vaccination.
