I also found this:
A recent paper published in the journal Clinical Infectious Diseases suggested that tetanus and diphtheria booster vaccines are not necessary for adults who have completed their childhood vaccination series. This advice aligns with the current World Health Organization (WHO) recommendations. The researchers reviewed WHO data from 31 North American and European countries between 2001 and 2016, amounting to 11 billion person-years. (Person-years is a measurement that reflects the number of people in the study multiplied by years followed). After comparing the incidence of tetanus and diphtheria, they found no significant difference in disease rates in countries that require adults to receive booster shots compared with those that do not. Based on this, the authors suggest that childhood vaccination alone protects sufficiently against tetanus and diphtheria without booster shots.
https://academic.oup.com/cid/article-abstract/72/2/285/5741633
(post is archived)