Vitamin C seems to be what most animals on this planet use as general anti-viral. It also seems it works in humans in mega dozes and/or IV. In any case "genera

Vitamin C seems to be what most animals on this planet use as general anti-viral. It also seems it works in humans in mega dozes and/or IV. In any case "general antiviral" seems to be even worst thing then general antibiotic. Most of bacteria / viruses are commensal, you don't really want to disturb that. For example, bacteriophage viruses are now known to handle some of the 100% resistant bacteria in a matter of days. IMO, the system is so complex that you should only support the crew that know how to handle that - i.e. your immune system - by providing resources they need (vitamins etc.) and avoid things detrimental for them (sugar, tonsillectomy etc.).