This disclosure relates to the prevention and treatment of Influenza, and more particularly Influenza A Virus Subtype H1N1, with the use of a pharmaceutical composition comprising one or more digestive enzymes, such as pancreatic enzymes and porcine pancreatic enzymes. The disclosure further relates to the use of an individual's fecal chymotrypsin level as an indicator, e.g., biomarker of whether an individual may be more susceptible to Influenza, e.g., Influenza A Subtype H1N1, and/or whether an individual will benefit from administration of the described pharmaceutical compositions. Use of the compositions as sanitizers, antiseptics, disinfectants, and detergents, e.g., to reduce or eradicate influenza virus present on living or inanimate surfaces is also contemplated.