Effect of simultaneous BCG and smallpox vaccination in schoolchildren. Report of a WHO-sponsored preliminary study.

The effect of simultaneous BCG and smallpox vaccination and the possible interaction of primary BCG vaccination and smallpox revaccination were studied in 1099 Burmese children arbitrarily allocated to four groups. All were tuberculin-tested and all had received primary smallpox vaccination but had not been vaccinated with BCG. In the first group, no vaccination was performed; in the second, negative reactors received BCG vaccine; the third received smallpox vaccine; and the fourth also received smallpox vaccine, negative reactors also receiving BCG vaccine.Comparison of the "take" of smallpox revaccinations in the third and fourth groups and the post-vaccination tuberculin allergy in the second and fourth groups gave no suggestion of interaction.There was no difference in the take of smallpox revaccination between tuberculin-negative and tuberculin-positive children, nor did smallpox vaccination influence naturally acquired tuberculin allergy.Smallpox revaccination had no apparent effect on the frequency distribution of BCG vaccination lesions, and further smallpox revaccination after one year showed that BCG vaccination had not influenced smallpox immunity.