Two potential improvements to BCG and their effect on skin test reactivity in the Lebanon

An account of an ongoing project to assess the possible benefits of two additives to BCG vaccine is presented. These additives are suspensions of irradiation killed Mycobacterium vaccae in one case, and M. leprae in the other. Groups of children aged 7-17 living in Zgharta and Akkar districts of North Lebanon have received vaccination with BCG alone or with either of the two additives since 1980. This region was chosen since contact with environmental mycobacteria is small, but both leprosy and tuberculosis occur there. So far the effects of the additives have been assessed by annual skin testing of volunteers with Tuberculin, Leprosin A, Vaccin and Scrofulin, and by measuring the size of the vaccine scars. Some children have now been followed up on four occasions, and special attention is paid to them. No complications have been encountered in the 1740 children who have entered the study (by our observation, or by local report on those who have not attended for follow-up) and the mean scar sizes after vaccines with the additives are no larger than those after BCG alone. There is no evidence that the additives have prevented development of Tuberculin positivity after vaccination, or have changed the nature of reaction to it. Incorporation of M. leprae significantly increased Leprosin A positivity and both additives increased Vaccin positivity in comparison with the effects of BCG alone. The results are fitted to a model of the theoretical expectations of the study and may be beginning to show the advantages expected of the additives. The only unexpected finding was a reduction in Scrofulin positivity especially associated with the additives. The very low contact with environmental mycobacteria experienced in the study area has allowed the pattern of post-vaccination decay of skin test positivity to be studied with greater precision than has been reported before, and differences have been detected between the two districts where the study was conducted. Confirmation of the possible advantage of the additives will rest with data to be obtained in longer term follow-ups and in studies being carried out in other countries.