Basic reproduction number

In epidemiology, the basic reproduction number (sometimes called basic reproductive rate or basic reproductive ratio) of an infection is the mean number of secondary cases caused by an individual infected soon after disease introduction into a population with no pre-existing immunity to the disease in the absence of interventions to control the infection. It is often denoted R₀. This metric is useful because it helps determine whether or not an infectious disease can spread through a population. The roots of the basic reproduction concept can be traced through the work of Alfred Lotka, Ronald Ross, and others, but its first modern applicationin epidemiology was by George MacDonald in 1952, who constructed population models of the spread of malaria.

When

R₀ < 1

the infection will die out in the long run (provided infection rates are constant). But if

R₀ > 1

the infection will be able to spread in a population.

Generally, the larger the value of R₀, the harder it is to control the epidemic. For simple models, the proportion of the population that needs to be vaccinated to prevent sustained spread of the infection is given by 1&nbsp;&minus;&nbsp;1/R₀. The basic reproductive rate is affected by several factors including the duration of infectivity of affected patients, the infectiousness of the organism, and the number of susceptible people in the...
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