Just for extra comfort from a BTDT momma... my ds is very prone to ingrown big toe nails. His daddy gets them ALL the time too. Ds has had no tetanus vax and he's still a healthy thriving growing boy. One did get pretty ingrown when he was about 2 so we saw our FP who had us do a round of abx to help it ease up. It did calm the infection and it healed up well.
One thing I have done if he gets them now is leave them alone. When he was young we would try to pull the nail up and out. Looking back that made it more agravated cause we were introducing foreign contaminants... letting them be has meant they heal pretty quickly.
Our doc also gave us a print out of how to cut his nails better and that has helped alot. Only cutting straight across and not down short or rounding off the nail has helped tremendously. I try to wait to trim his nails til they are pretty long now and just trim right across the top.
There are thousands of little booboos that "could" set up with tetanus and if you read about all of them you'll be sitting in a corner rocking and sucking your thumb soon. Try not to focus on it. Even prevax tetanus was not a major health problem and that was back when people were out in the barn yard and working and not able to wash up, etc. Access to wound care has reduced the occurence way more than the vax I would venture to guess.