In this work, a mathematical model for describing
diphtheria transmission in Thailand is proposed. Based on the course of
diphtheria infection, the population is divided into 8 epidemiological classes, namely, susceptible, symptomatic infectious, asymptomatic infectious, carrier with full natural-acquired immunity, carrier with partial natural-acquired immunity, individual with full
vaccine-induced immunity, and individual with partial
vaccine-induced immunity. Parameter values in the model were either directly obtained from the literature, estimated from available data, or estimated by means of sensitivity analysis. Numerical solutions show that our model can correctly describe the decreasing trend of
diphtheria cases in Thailand during the years 1977-2014. Furthermore, despite Thailand having high
DTP vaccine coverage, our model predicts that there will be
diphtheria outbreaks after the year 2014 due to waning immunity. Our model also suggests that providing booster doses to some susceptible individuals and those with partial immunity every 10 years is a potential way to inhibit future
diphtheria outbreaks.