Epidemiological Pattern and the Dynamics of Diphtheria Outbreak in Nigeria(A SIR and SEIR Modeling Approach)

Abstract

Diphtheria is highly prevalent in the African countries especially among the Sub-Saharan Africa. Factors such as declining herd immunity due to low vaccination are key determinants of the outbreak in Nigeria, while the high mortality rate recorded has been attributed to the non-availability of diphtheria antitoxin (DAT). Hence, this study examined the dynamics of the spread of diphtheria in Nigeria during the epidemic period using the SIR and SEIR Modeling approach with a set of data collated monthly from the monthly publications of the NCDC. The results of the SIR model revealed value of 0.14 estimated for the transmission rate suggesting moderate transmission rate, and removal rate of 0.50 which indicated a 50% chance of recovery, death, or complete removal from the entire population. Also, results of SEIR Model revealed estimated value of 0.42 for the transmission rate suggesting moderate rate of spread with an average latent period of 5 days. The computed average reproduction rate for SIR model was approximately 0.28 while that of SEIR model was approximately 0.84 since R0 <1, this indicates that one infected individual cause less than 1 new infection which can further be explained as a maximum control in the rate of spread. However, the computed value of herd immunity obtained for the SIR model was 0.72 while 0.16 was estimated for SEIR Model. Since both estimated values of herd immunity are lower than 80%, it indicates that an insignificant portion of the susceptible population is yet to develop strong immunity against diphtheria infection.