1.2 Understanding R₀

The basic reproduction number (R₀) is important because it encapsulates the relationship between an infection and its physical and social environment.

The number of secondary infections depends on the ability of the infectious organism to survive outside the host and to migrate from one host to the next, which in turn is contingent on biological and environmental factors. It depends on the infection–host interaction through, for instance, the duration of the infectious period. It is also affected by the frequency and type of contacts that take place within the population, which vary according to environmental, social and cultural factors.

R₀ can also tell us about how quickly an infection is likely to grow in an unvaccinated, fully-susceptible population. Table 1 shows R₀ values for a number of virus diseases, Note that the values given are ranges, which will vary depending on the population and how the communities interact.

As you can see SARS-CoV2 falls around the middle of the range for virus diseases, but as it turned out different variants of SARS-CoV2 have different R₀ values.