I last had a single tetanus jab in London about 25 years ago, while I had M.E. It flared everything up intensely (not just a sore arm - I was really ill). They measured my antibodies and they were the same as someone who'd had about 5 jabs all at once, or had been exposed to tetanus (I hadn't). I remember the doctor suggesting that I was one of those weird people who visit hospitals for multiple in inoculations
Eventually my SA GP told me no more tetanus boosters, but if I was exposed I should take antibiotics. That was in South Africa where the risk of tetanus is far higher than the UK, where it's very rare. I have heard that the tetanus inoculation is a particularly nasty one.
I still think about it when I **** myself on a rose bush mind you