Mutant virus, preparation method therefor and application thereof

A pharmaceutical composition comprising a mutated influenza virus, which is characterized in that a coding nucleic acid of at least one protein of the virus comprises one or more UAG codons at a position located one or more codons upstream of a natural, endogenous stop codon of the coding nucleic acid;

• wherein the at least one protein of the virus is selected from PA, PB1, PB2, or NP protein, and the at least one protein in the virus comprises an unnatural amino acid at the position corresponding to the one or more UAG codons, wherein the influenza virus comprises UAG codon(s) at positions of codon(s) of nucleic acid(s) encoding R266 of PA protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:4, R52 of PB1 protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:3, K33 of PB2 protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:2, and/or D101 of NP protein by reference to a corresponding amino acid encoded by a nucleic acid as set forth in SEQ ID NO:6, wherein the composition is an active influenza virus vaccine, wherein the vaccine is capable of eliciting an immune response.