The present invention provides peptides, peptide analogs, peptide derivatives and pharmaceutical compositions useful for treating or preventing influenza infections or preventing the person-to-person transmission of an influenza infection. A peptide of the invention comprises an influenza virus-cell fusion inhibiting portion of the fusion initiation region (FIR) of a wild-type influenza hemagglutinin 2 protein or a variant thereof. In a preferred embodiment, a peptide of the invention consists of 8 to 40 consecutive amino acid residues a portion of a wild-type influenza hemagglutinin 2 protein or a variant thereof, the portion of the protein comprising the FIR of the protein and up to five amino acid residues on the amino-terminal and carboxy-terminal sides of the FIR.
