In epidemiology, the basic reproduction number of an infection is the mean number of secondary cases a typical single infected case will cause in a population with no immunity to the disease in the absence of interventions to control the infection. It is often denoted R₀ .

When

R₀ < 1

the infection will die out with certainty. But if

R₀ > 1

there is some possibility of a major epidemic.

Generally, the larger the value of R₀, the harder it is to control the epidemic. In particular, the proportion of the population that need to be vaccinated to provide herd immunity and prevent sustained spread of the infection is given by 1-1/R₀.

Values of R₀ of some well-known infectious diseases:

• SARS: 2-5
• AIDS: 2-5
• Measles: 16-18
• Influenza 2-3

Epidemiology

reproductiegetal | 基本传染数