Influenza virus hemagglutinin mutants

A modified influenza H1 hemagglutinin (HA) protein comprising an HA amino acid sequence of an influenza H1 strain, wherein the HA amino acid sequence comprises amino acid substitutions when compared to a wildtype HA amino acid sequence of the same influenza H1 strain, wherein the amino acid substitutions correspond to the following positions:

• i) positions 390 and 429 of reference sequence SEQ ID NO:
• 134;
• ii) positions 390, 429 and 97 of reference sequence SEQ ID NO:
• 134, wherein the wildtype HA amino acid sequence comprises any amino acid aside from aspartic acid (D) at position 97 and the substitution at position 97 converts the amino acid to any amino acid aside from asparagine (N) when the wildtype amino acid is N97;
• iii) positions 390, 429 and 374 of reference sequence SEQ ID NO:
• 134, wherein the wildtype HA amino acid sequence comprises any amino acid aside from glutamic acid (E) at position 374 and the substitution at position 374 converts the amino acid to any amino acid aside from lysine (K) when the wildtype amino acid is K374;
• and
• iv) positions 390, 429, 97 and 374 of reference sequence SEQ ID NO:
• 134, wherein the wildtype HA amino acid sequence comprises any amino acid aside from aspartic acid (D) at position 97 and the substitution at position 97 converts the amino acid to any amino acid aside from asparagine (N) when the wildtype amino acid is N97, and wherein the wildtype HA amino acid sequence comprises any amino acid aside from glutamic acid (E) at position 374 and the substitution at position 374 converts the amino acid to any amino acid aside from lysine (K) when the wildtype amino acid is K374.