Abstract: The present invention relates to a genetic engineering process for the optimal production and exposure to the immune system of additional antigen coded for by a live vaccine. The genetic engineering process is based on the use of spontaneous DNA reorganisation in the recombinant live vaccine, such that the recombinant live vaccine spontaneously divides into two subpopulations (A and B), whereby subpopulation A is capable of infecting and acts immunogenically per se as a minimum characteristic and subpopulation B as a minimum characteristic is regenerated by subpopulation A, produces additional antigen and acts immunogenically with respect to said additional antigen.