Rodents and rabbits don't have the ability to vomit. In fact you can feed them on days when anesthetic is administered because there is no risk of aspiration like there is with cats and dogs. The effects of some viruses might be diarrhea or loose stools, loss of appetite, that sort of thing if there are any symptoms. Burnt toast can be used as a remedy for loose stools. Stomach irritation will usually present with loss of appetite. If there is serious diarrhea to the point where you need to clean it up you will need to have an emergency vet visit. Again the risk is very low. Gastro-intestinal viruses are not airborne and only select viral strains can be transmitted across species. Respiratory infections you might need to be more careful with since secondary bacterial infections are often concurrent and bacteria is easily transmitted across species.