Some evidence of the efficacy of mass BCG vaccination.

To assess the efficacy of mass BCG programmes the authors have made a comparative analysis of age-specific trends in the incidence of active tuberculosis in the three Scandinavian countries, where mass vaccination of specific age-groups has been carried out since the late 1940s, and two states of the USA (upstate New York and Ohio), where mass BCG campaigns have never been conducted.In the three Scandinavian countries a markedly more favourable incidence trend was observed in the age-groups following the first inoculation-as compared with other age-groups in the same country and with corresponding age-groups in the other countries where a different BCG programme, or no programme at all, has been applied. The authors consider that these observed differences in incidence trends reflect the influence of BCG vaccination and, on this assumption, have attempted to estimate the primary effect of the BCG programmes quantitatively, in terms of hypothetical "gained and lost cases" in the various age-groups. They stress, however, that the significance of these gained and lost cases must be evaluated from an epidemiological viewpoint and that the relevant epidemiological factors must be taken into account in the planning of BCG programmes.