Shows require QT periods, as well as health checks. Judges routinely wash their hands or sanitize at mouse shows. Mice are known for being disease carriers and mite hosts, but it is extremely rare for a mouse to catch something durring a show, other than possibly sniffles which can be caused simply by the stress of being driven to and from the show.
It's something that ANYONE who shows ANY species has to come to terms with. Dog breeders and cat breeders could pass all kinds of deadly viruses and diseases back and forth between their animals, but most of the time things are carried out as safely as possible, and disaster is avoided every time.
Rabbits, pigeons, mice, cavies, chinchillas, there are no vaccine requirements for these animals, and they are shown often. Rats are another good example of excelent carriers for all kinds of uglies, but people show them often, and rarely RARELY have problems, when QT and health check is done.