Answer
If tetanus and diphtheria vaccinations need to be restarted, the schedule is as follows: a first dose, a second dose one month later, and a third dose one year after the first. This is the sequence specified for resuming vaccination.
This schedule matters for people who do not have records of past vaccinations or cannot verify when they were administered. The process does not end with the first dose: remember the second dose one month later and the third dose one year after the first.
In practice, this means vaccination should not be treated as a one-visit matter. Once the schedule has begun, record the dates for subsequent doses right away so that the local certificate reflects the full course rather than just the initial vaccination, and you will not have to figure out the schedule again later.