I always thought the standard of tetanus shots was every 10 years, but now hear that it is 5. did it change, and if so why?

Really dirty wound: Need tetanus shot if you haven't had one in last 10 years, don't know when you last had one or if the wound is dirty & it has been more than 5 years since last shot. See: http://www.mayoclinic.org/first-aid/first-aid-cuts/basics/art-20056711

Tetanus vaccination: The current guidelines still recommend tetanus booster shots every 10 years, which is the usual time frame that your protection wears off. It is also administered whenever the is an puncture or laceration wound & question of whether or not the tetanus vaccination is up to date. Hope this helps & continue to ask questions when you have them.

Tetanus: It's 10 years between boosters UNLESS you have a dirty wound and it's been 5 or more years since your last booster, then they recommend getting it earlier.

10 years if no cuts: If a dirty cut or a puncture wound need a booster after 5 years.