Influenza hemagglutinin and neuraminidase variants

1. A 6:2 reassortant influenza B virus, wherein said virus comprises 6 internal genome segments from one or more donor viruses and two surface antigen genome segments, wherein the surface antigen genome segments encode an HA and a NA polypeptide, and wherein the HA polypeptide comprises the amino acid sequence of SEQ ID NO: 93.

2. The 6:2 reassortant influenza B virus of claim 1 , wherein said one or more donor viruses comprise one or more of the following phenotypes: temperature-sensitive, cold-adapted, or attenuated.

3. The 6:2 reassortant influenza B virus of claim 1 , wherein said one or more donor viruses are selected from the group consisting of B/Ann Arbor/1/66, B/Leningrad/14/17/55, B/14/5/1, B/USSR/60/69, B/Leningrad/179/86, B/Leningrad/14/55, and B/England/2608/76.

4. The 6:2 reassortant influenza B virus of claim 1 , wherein said reassortant influenza B virus is killed or inactivated.

5. The 6:2 reassortant influenza B virus of claim 1 , wherein said reassortant influenza B virus is a live attenuated reassortant influenza B virus.

6. An immunogenic vaccine composition comprising an immunologically effective amount of the reassortant influenza B virus of claim 2 .

7. An immunogenic vaccine composition comprising an immunologically effective amount of the reassortant influenza B virus of claim 4 .

8. An immunogenic vaccine composition comprising an immunologically effective amount of the reassortant influenza B virus of claim 5 .

9. A method for stimulating the immune system of an individual to produce a protective immune response against influenza B virus, the method comprising administering to the individual an immunologically effective amount of the reassortant influenza B virus of claim 2 in a physiologically effective carrier.

10. A method for stimulating the immune system of an individual to produce a protective immune response against influenza B virus, the method comprising administering to the individual an immunologically effective amount of the reassortant influenza B virus of claim 4 in a physiologically effective carrier.

11. A method for stimulating the immune system of an individual to produce a protective immune response against influenza B virus, the method comprising administering to the individual an immunologically effective amount of the reassortant influenza B virus of claim 5 in a physiologically effective carrier.

12. A method of prophylactic or therapeutic treatment of a influenza B viral infection in a subject, the method comprising: administering to the subject the reassortant influenza B virus of claim 2 in an amount effective to produce an immunogenic response against the influenza B viral infection.

13. A method of prophylactic or therapeutic treatment of a influenza B viral infection in a subject, the method comprising: administering to the subject the reassortant influenza B virus of claim 4 in an amount effective to produce an immunogenic response against the influenza B viral infection.

14. A method of prophylactic or therapeutic treatment of a influenza B viral infection in a subject, the method comprising: administering to the subject the reassortant influenza B virus of claim 5 in an amount effective to produce an immunogenic response against the influenza B viral infection.

15. The method of claim 12 , wherein the subject is a human.

16. The method of claim 13 , wherein the subject is a human.

17. An immunogenic vaccine composition comprising an immunologically effective amount of the reassortant influenza B virus of claim 1 , wherein the reassortant influenza virus is a split virus.

18. The immunogenic vaccine composition of claim 6 , wherein the reassortant influenza virus is a split virus.

19. The immunogenic vaccine composition of claim 7 , wherein the reassortant influenza virus is a split virus.

20. A method for producing an influenza B virus in cell culture, the method comprising:

i) introducing into a population of host cells, which population of host cells is capable of supporting replication of influenza virus, a plurality of vectors comprising nucleotide sequences corresponding to:

(a) at least 6 internal genome segments of one or more donor viruses, and at least one genome segment encoding an HA surface antigen polypeptide, wherein the surface antigen polypeptide comprises the amino acid sequence from SEQ ID NO: 93; or

(b) at least 6 internal genome segments of one or more donor viruses, which one or more donor viruses comprises one or more phenotypic attributes selected from the group consisting of: attenuated, cold adapted and temperature sensitive; and at least one genome segment encoding an HA surface antigen, wherein the surface antigen polypeptide comprises the amino acid sequence of SEQ ID NO: 93;

ii) culturing the population of host cells at a temperature less than or equal to 35° C.; and,

iii) recovering influenza virus.