BCG vaccination and the incidence of lymphomas and leukaemia

BCG vaccination has been claimed to prevent leukaemia, but there is also concern that it might increase the risk of Hodgkin's disease and other lymphomas. Both hypotheses were tested by comparing mortality and registration rates in cohorts of children from the North and South Islands of New Zealand. When school-children were offered vaccination in both islands, subsequent death rates from lymphomas and leukaemia were similar in the two islands. After withdrawal of vaccination in the South Island, mortality and registration rates for Hodgkin's disease remained similar in the two islands, but there was significant excess of deaths from non-Hodgkin lymphomas in the North Island. The difference in the registration rates for these tumours was much smaller than the difference in mortality rates and was not statistically significant. There was no evidence that BCG vaccination in the North Island prevented leukemia. These findings and the results of other studies suggest that proposals for BCG vaccination against leukaemia are unwise.