Influenza hemagglutinin and neuraminidase variants

A method for producing reassortant influenza viruses in cell culture, the method comprising:

• i) introducing a plurality of vectors comprising polynucleotides corresponding to an influenza virus genome into a population of host cells capable of supporting replication of influenza virus, which plurality of vectors comprises polynucleotides corresponding to at least 6 internal genome segments of a first influenza strain, and at least one genome segment of a second influenza strain, wherein the at least one genome segment of the second influenza strain comprises a polynucleotide comprising a nucleotide sequence encoding the amino acid sequence of SEQ ID NO:
• 39;
• ii) culturing the population of host cells;
• and
• iii) recovering a plurality of influenza viruses.