Methods and systems for virus inactivation in the production or processing of biological or other sensitive substances are provided. The disclosed methods and systems for virus inactivation involve the key steps of dissolving carbon dioxide into biological or other sensitive substances and treating the substance with the dissolved carbon dioxide at conditions which are less than critical pressure and temperature for a prescribed treatment time to inactivate at least 80% of the target virus or viruses contained within the biological or other sensitive substances. The disclosed carbon dioxide treatments for virus inactivation may optionally include concurrently or sequentially subjecting the substances with an acid treatment to lower the pH of the substance and inactivate viruses contained within the biological or other sensitive substance. Operating conditions for the disclosed carbon dioxide treatments preferably involve sparging carbon dioxide gas into the substance until the composition is saturated with carbon dioxide and is conducted at pressures below about 5 MPa at temperatures of less than or equal to 30° C. and for a treatment time of between about one minute and about 2000 minutes.
