Abstract: The present invention provides methods for the treatment of an ongoing influenza infection by administering a polypeptide to a subject suffering from an influenza infection. The polypeptide consists of SEQ ID NO: 4. The present invention also provides a method of interfering with fusion of an influenza virus envelope with a host cell membrane by contacting the host cell with a polypeptide consisting of SEQ ID NO: 4.

Abstract: The present invention provides compositions useful for treating or preventing influenza infections. The composition comprises an isolated polypeptide including a sequence of at least 8 contiguous amino acid residues of the fusion initiation region (FIR) of an influenza hemagglutinin 2 protein or a peptide analog of the sequence. The FIR is a segment of the full length hemagglutinin 2 protein which is bounded by an amino-terminal region within the amino-terminal alpha-helix thereof and a carboxy terminus within the carboxy-terminal alpha-helix thereof, with a cysteine loop therebetween. The amino-terminal region of the FIR comprises a portion of the final 10 to 20 amino acid residues of the amino-terminal alpha-helix of the hemagglutinin 2 protein, and includes 3 or 4 hydrophobic amino acid residues, a positively-charged amino acid residue, a negatively-charged amino acid residue, and an aromatic amino acid residue.