Conditions for production of thermosensitive attenuated influenza virus recombinants.

Recombination and cross-reactivation between virulent influenza viruses and a cold-adapted thermosensitive vaccine strain regularly produced genetically stable attenuated recombinants, the selection of which was based on the thermosensitivity marker. This marker, correlating with the safety of the recombinants for man was inherited independently on the properties of the haemagglutinin and neuraminidase surface antigens. There was no relationship between the thermosensitivity of the resulting recombinants and the decrease in the optimal temperature of the neuraminidase activity (OTNA marker). This indicates a separate localization in the viral genome of the mutation damages responsible for the expression of ts and OTNA markers.