The Failure of 𝑅₀

Figure 1

A example of a two-stage basic reproductive ratio. A single human infects 𝑅_𝐻=2 mosquitoes, each of whom subsequently infects 𝑅_𝑀=3 humans. Thus, a single human results in 𝑅₀=6 infected humans. The next-generation method instead estimates 𝑅_0,𝑁=√6 infected individuals in the subsequent generation, regardless of whether that generation is human or mosquito; 𝑅_0,𝑁 is the geometric mean of 𝑅_𝐻=2 and 𝑅_𝑀=3. (Reproduced with permission from Smith? [7]).