The invention provides methods of producing vaccines directed against microorganisms, with the methods comprising culturing, harvesting and/or suspending the microorganism in the presence of a radiation-protective composition and irradiating the bacteria or viruses with a dose of radiation sufficient to render the microorganism replication-deficient and/or non-infective. The radiation-protective compositions used in the methods of the present invention comprise at least one nucleoside, at least one antioxidant and at least one small peptide. The invention also provides methods of rendering bacteria in culture resistant to ionizing radiation (IR), with these methods comprising culturing the bacteria in the presence of a radiation-protective composition.