Keep your boosters up to date. I went through a nasty bout with whooping cough a few years ago. Since I came back stateside I had not thought to get boosters. Now I do. Too soon old and too late smart.
Tetanus is a bit weird.
Cases are VERY rare nowadays. The US recommendation for new vaccination booster is 10 yrs. The Brits for quite some time said if you got a booster in your early 20s, you were good for life. The antibody level in the body is hard to measure but residual immunity does exist for people who were vaccinated in their 20s and not since.
Standard procedure in all ERs for any wound is a booster, if you do not remember or are sure it has been 10 yrs.
Ex military essentially never get it, because they are sure to have been vaccinated in their early 20s.
The few cases typically seen are nursing home very elderly. The residual immunity has just faded too much from 20s to 80s.
It sounds like your friend had some immunity but there was soooo much injected bacteria that it was overwhelming it. A booster and antitoxin should take care of it.