Beaniemaster 2. Tetanus shots are immunizations--like measles or the flu. It keeps you from getting tetanus. You should get a booster tetanus immunization, at least every 10 years. I would suggest trying to get one about every 7 years so you'll have a window of immunity if a disaster hits.
Your doctor can give you one or, probably the health department. Most tetanus shots will be combine with a diptheria and, possibly, pertussis--two contagious diseases which will certainly be more prevalent in prolonged disasters.