improved reverse genetics methods for the recovery of virus

Method of preparing a virus comprising the steps of (i) transfecting a host cell culture with at least one expression construct encoding a molecule of viral RNA, (ii) addition of cells to host cells transfected (i ) to provide a mixture of cells, in which the host cells and cells added after transfection are of the same cell line, and (iii) culturing the mixture of cells in order to produce a virus.