Not sure of the risk, but when I stepped on a nail in March (9 to 10 years since last Tetanus shote), I made sure it was cleaned out really well. I took the homeopathic remedies that my homeopath had previously mentioned were good for Tetanus---Ledum and Hypericum (I have read someone here say you shouldn't just take them, but make sure they fit the case--I did just take both). I also took high doses of vitamin c (well high form me--6,000 to 10,000 grams a day--can't really remember). Here is a link I found just now when googling how to spell ledum and hypericum--maybe it would be helpful to you (didn't read any of it, but bookmarked to look at later).
http://www.suite101.com/reference/te...edum_hypericum