1. Beare, A. S., Maassab, H. F., Tyrrell, D. A. J., Slepushkin, A. N., Hall, T. S.: A comparative study of attenuated influenza viruses. Bull. WHO44, 593?598 (1971).
2. Boudreault, A., Lussier, G., Pavilanis, V.: Caracteres biologiques de souches du virus de l'influenza adaptees a 29° C et a 41° C. Canad. J. Microbiol.14, 867 to 874 (1968).
3. Davenport, F. M., Hennessy, A. V., Minuse, E., Maassab, H. F., Anderson, G. R., Mitchel, J. R., Heffelfinger, J. C., Barret, C. D., Jr.: Pilot studies on mono and bivalent live attenuated influenza virus vaccines. In: Proc. Symp. Live Influenza Vaccine, 105?113. Zagreb: Yugoslav. Acad. Sci. Arts. 1962.
4. Karber, G.: Method Described. In:Lennette, E. H., Schmidt, N. J. (eds.), Diagnostic Procedures for Viral and Rickettsial Infections, 4th ed., 49?52. New York: American Public Health Assoc., Inc. 1969.
5. Kendal, A. P., Kiley, M. P.: Characterization of influenza neuraminidase: Peptide changes associated with antigenic divergence between early and late N2 neuraminidases. J. Virol.12, 1482?1490 (1973).