Tetanus or lockjaw is a serious illness caused by the toxin of the bacterium Clostridium tetani. The soil and animal intestines contain large amounts of the bacteria. E.g. animal bites and wounds contaminated by soil or sand can lead to Clostridium infection.
Tetanus bacteria multiply in the wound and produce a neurotoxin that is transported into the central nervous system and can cause respiratory depression. The vaccination is included in the National Vaccination Programme: a basic vaccination series in childhood is followed by booster shots for working age adults with 20 year intervals, and with 10 year intervals for people over 65 years of age.
Tetanus is not transmitted between persons, which is why there is no protection from herd immunity, and each individual must take care of their own vaccination safety ward off the disease.
Having contracted tetanus once does not protect from a new infection either.