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When $R_0 > 1$, each generation of infections is larger than the previous one because every case produces more than one new infection on average. This repeated multiplication by a factor greater than one results in exponential growth of the outbreak.

Conditions: Assumes the same average transmission per case across generations.; The worked example uses $R_0=2.5$.

When $R_0 > 1$, each generation of infections is larger than the previous one because every case produces more than one new infection on average. This repeated multiplication by a factor greater than one results in exponential growth of the outbreak.

Conditions: Assumes the same average transmission per case across generations.; The worked example uses $R_0=2.5$.

The basic reproduction number, denoted $R_0$, is defined as the average number of new infections caused by a single case in a population where everyone is susceptible. It serves as an early-outbreak measure of transmission potential.

Conditions: Applies to a population where everyone is susceptible.; Used here as an early-outbreak measure.

The basic reproduction number, denoted $R_0$, is defined as the average number of new infections caused by a single case in a population where everyone is susceptible. It serves as an early-outbreak measure of transmission potential.

Conditions: Applies to a population where everyone is susceptible.; Used here as an early-outbreak measure.