Clinically severe diphtheria is caused by toxin-producing (toxigenic) strains of Corynebacterium diphtheriae. Infection with toxigenic diphtheria strains is extremely rare in New Zealand (NZ), but they continue to circulate elsewhere in the world, so there is a risk of importation through international travel particularly from South-East Asia. Globally, immunity in young children has dramatically improved through targeted immunisation programmes, and as a result, from 1998 to 2000 reported diphtheria cases decreased by more than 90% globally. However, diphtheria remains a substantial cause of morbidity and mortality in countries with incomplete or disrupted childhood immunisation programmes. Around 14% of children worldwide are not fully immunised against diphtheria and all countries have variable-sized pockets of unvaccinated children. This is a review of literature published between January 2015 and July 2019 focussing on questions relevant to diphtheria immunisation in NZ. The evidence presented has not been formally graded as in a systematic review, and cost effectiveness of pneumococcal vaccines is not included.