γ-Irradiation of the BCG vaccine will be performed by Synergy Health Ede B.V., Ede, The Netherlands (registered by the Dutch Ministry of Economic Affairs). The BCG vaccine was radiated in the original packaging with an average dose of 32.2kGy in a JS6500 Tote Box Irradiator. This dose is based on an in the literature accepted minimal dose of 25kGy, which has been proven to be sufficient to kill M. tuberculosis [10, 11] . After irradiation the vaccine will be returned unopened in the original packaging. During the irradiation a dosimeter is included, so each irradiated batch will come along with a certificate with the exact irradiation dose used.