Abstract: A pharmaceutical composition for treating or preventing influenza comprising an oligonucleotide containing a base sequence complementary to a base sequence of a target region containing a translational initiation codon AUG of a PB2 gene or a PA gene, a liposome stable in blood, and a pharmaceutically acceptable carrier or dilute is disclosed. The pharmaceutical composition for treating or preventing influenza can be used in an effective treatment of or prevention of an infection by influenza viruses.

Abstract: A pharmaceutical composition comprising a capped oligonucleotide capable of binding to a PB2 protein of an influenza virus RNA polymerase, and a pharmaceutically acceptable carrier or dilute, said capped oligonucleotide having a structure of the formula (I): m7GpppXpY  (I) wherein ppp is a triphosphate bridge, p is a monophosphate bridge, m7G is 7-methylguanosine group binding at 5′ end thereof to said ppp, X is a 2′-O-methyl guanosine group or guanosine group, said 2′-O-methyl guanosine group or guanosine group binds at a 5′ end thereof to said ppp, and at a 3′ end thereof to said p, and Y is an oligoribonucleotide moiety binding at 5′ end thereof to said p, and having 5 to 11 bases is disclosed. The pharmaceutical composition can inhibit a protein expression of an influenza virus.