## Abstract

The phenomenon of backward bifurcation in disease models, where a stable endemic equilibrium co-exists with a stable disease-free equilibrium when the associated reproduction number is less than unity, has important implications for disease control. In such a scenario, the classical requirement of the reproduction number being less than unity becomes only a necessary, but not sufficient, condition for disease elimination. This paper addresses the role of the choice of incidence function in a vaccine-induced backward bifurcation in HIV models. Several examples are given where backward bifurcations occur using standard incidence, but not with their equivalents that employ mass action incidence. Furthermore, this result is independent of the type of vaccination program adopted. These results emphasize the need for further work on the incidence functions used in HIV models.

Original language | English (US) |
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Pages (from-to) | 436-463 |

Number of pages | 28 |

Journal | Mathematical Biosciences |

Volume | 210 |

Issue number | 2 |

DOIs | |

State | Published - Dec 2007 |

Externally published | Yes |

## Keywords

- AIDS
- Backward bifurcation
- Equilibrium
- HIV
- Mass action incidence
- Mathematical model
- Stability
- Standard incidence
- Vaccine

## ASJC Scopus subject areas

- Statistics and Probability
- Modeling and Simulation
- General Biochemistry, Genetics and Molecular Biology
- General Immunology and Microbiology
- General Agricultural and Biological Sciences
- Applied Mathematics