In most cases, no special vaccinations are required though you should make sure you are up to date with tetanus and other basic inoculations. The Center for Disease Control and Prevention has additional health information for travelers to Nicaragua, including recommended vaccinations.
If you are taking any medications, it’s best to bring as many as you need for your trip. In case of loss keep a note of the active ingredients and not just the brand name. A copy of your prescription is also a good idea.