This paper examines the dynamics of Hepatitis B via a Susceptible Exposed Infectious Recovered (SEIR) type epidemic model. Previous studies have shown that Hepatitis B is characterized by multiple endemic solutions, a matter which may be of concern in developing control strategies. We identify the possible causes of multiple endemic solutions in a Hepatitis B model and conclude that the dependance of the probability of carriage development (q(Λ)) on the force of infection (Λ) is the main reason for multiple endemicity. Other factors such as a large proportion of infants that are not vaccinated (ω) may also enhance the possibility of multiple endemicity. The role of carriers may also play a key role in the possibility of such complex dynamics, i.e., when infectiousness of carriers-(α) is high, the probability of existence of multiple endemic equilibrium solutions is increased. In our arguments, the traditional reproduction number R0< 1 which we define here by a function G(0) < 1 does not imply stability of disease-free equilibrium.
 Kuznetsov, A.Y. (2004) Elements of Applied Bifurcation Theory. 3rd Edition, Springer, Berlin.
 Guckenheimer, J. and Holmes, P. (1983) Nonlinear Oscillations, Dynamical Systems and Bifurcations of Vector Fields. Springer, Berlin.
 Edmunds, W.J., Medley, G.F. and Nokes, D.J. (1996) The Transmission Dynamics and Control of Hepatitis-B Virus in the Gambia. Statistics in Medicine, 15, 2215-2233.
 Zhao, S., Xu, Z. and Lu, Y. (2000) A Mathematical Model of Hepatitis B Virus Transmission and Its Application for Vaccination Strategy in China. International Journal of Epidemiology, 29, 744-752.
 Inaba, H. (2006) Mathematical Analysis of an Age Structured SIR Epidemic Model with Vertical Transmission. Discrete and Continuous Dynamical Systems, Series B, 6, 69-96.
 Pruess, J. and Schappacher, W. (1984) Semigroup Methods for Age-Structured Population Dynamics. In: Chatterji, S., Fuchstainer, B., Kulisch, U. and Liedl, R., Eds., Jarbuch überblicke Mathematik, Viewing Verlag.
 Dietz, K. and Schlenze, D. (1985) Mathematical Models for Infectious Disease Statistics, a Celebration of Statistics. In: Atkinson, A.C. and Fienberg, S.E., Eds., The ISI Centenary Volume, Springer-Verlag, New York.
 Müller, J. (1998) Optimal Vaccination Patterns in Age-Structured Populations. SIAM Journal on Applied Mathematics, 59, 222-241.
 Inaba, H. (1990) Threshold and Stability Results for an Age-Structured Epidemic Model. Journal of Mathematical Biology, 28, 411-434.
 Diekmann, O., Heesterbeek, J.A.P. and Metz, J.A.J. (1990) On the Definition and the Computation of the Basic Reproduction Ratio R0 in Models for Infectious Diseases in Heterogeneous Populations. Journal of Mathematical Biology, 28, 365-382.
 Chavez, C.C. and Song, B. (2004) Dynamical Models of Tuberculosis and Their Applications. Mathematical Bioscience and Engineering, 1, 361-404.
 Hadeler, K.P. and Van den Driessche, P. (1997) Backward Bifurcation in Epidemic Control. Mathematical Biosciences, 146, 15-35.
 Sharomi, O., Podder, C.N., Gumel, A.B., Elbasha, E.H. and Watmough, J. (2000) Role of Incidence Function in Vaccine-Induced Backward Bifurcation in Some HIV Models. Mathematical Biosciences, 210, 436-463.
 Garba, S.M., Gumel, A.B. and Bakar, M.R.A. (2008) Backward Bifurcations in Dengue Transmission Dynamics. Mathematical Biosciences, 215, 11-25.
 Reluga, T.C., Medlock, J. and Perelson, A.S. (2008) Backward Bifurcations and Multiple Equilibria in Epidemic Models with Structured Immunity. Journal of Theoretical Biology, 252, 155-165.
 Robotin, M.C. (2011) Hepatitis B Prevention and Control: Lessons from the East and the West. World Journal of Hepatology, 3, 31-37.