# P646

“The basic reproductive number, *R _{0}*, is widely used in infectious disease research to estimate the transmission potential of a disease.

*R*is defined as the average number of secondary infections caused by a single infection, assuming that the population is completely susceptible and that there are no interventions. Generally, a disease with an

_{0}*R*value < 1 will eventually die out, while a disease with an

_{0}*R*value > 1 may continue to spread and trigger an epidemic. Average

_{0}*R*values for some common infectious diseases are listed in Table 1. In its simplest form,

_{0}**Equation 1**

*=*

R

R

_{0}*pcd*

where

*p*is the transmissibility of the disease,

*c*is the rate of contact with uninfected members of the population, and

*d*is the duration of contagiousness. In reality, a population may not be entirely susceptible and interventions may provide immunity to certain members of the population. Thus, the effective reproductive number,

*R*, is a means of relating

*R*to the actual level of susceptibility and is given by

_{0}

**Equation 2**

*=*

R

R

*R*

_{0}xwhere

*x*is the proportion of the population which is susceptible. One highly successful method of combating an outbreak is vaccination. The proportion of the population,

*V*, which would need to be vaccinated in order to reduce the effective reproductive number to < 1 is

**Equation 3**

*= 1 – (1/*

V

V

*R*)

_{0}Estimates of

*R*,

_{0}*R*, and

*V*are used to determine the appropriate level of intervention necessary to control infectious diseases.

Disease |
R0 |

Measles | 16 |

Diphtheria | 7 |

Smallpox | 6 |

Polio | 6 |

Mumps | 5 |

HIV | 4 |

SARS | 4 |

Ebola | 3 |

Influenza (1918) | 2 |

**Table 1**. Approximate

*R*values for common diseases.”

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