The present invention provides methods for treating or preventing influenza virus infection. The methods of the present invention comprise administering to a subject in need thereof a pharmaceutical composition comprising a type II transmembrane serine protease (TTSP) inhibitor. The TTSP inhibitor preferably functions by inhibiting the proteolytic cleavage of influenza hemagglutinin (HA0) into the functional subunits HA1 and HA2. In certain embodiments, the TTSP inhibitor is an inhibitor of transmembrane protease serine S1 member 2 (TMPRSS2), such as an anti-TMPRSS2 antibody or antigen-binding fragment thereof.
