Conditional Herd Immunity

The basic reproduction number, R0, for COVID-19 is estimated to be 2.5. With this level of R0, herd immunity is reached when 60% of the population have been infected or recovered. During the COVID-19 epidemic, governments are encouraging/ordering the population to vary their behavior so that the effective value of R is considerably less than 2.5. This raises the prospect of a population reaching herd immunity with only 20% of the population being infected or recovered. This would be conditional herd immunity as it would be conditional on the population maintaining the lower value of R even after the number of infections starts to drop.

Based on a detailed analysis we present the countries listed in order of the expected time to reach conditional herd immunity.

Rank Country Years to Herd Immunity Immunity (%) R values TII (ppm) Strategy
21 Peru -0.28 32.64 0.52 2984.34
22 Andorra -0.27 26.81 0.86 2174.43
23 Colombia -0.2 26.45 0.93 6730.84
24 Poland -0.16 30.28 0.72 2504.15
25 Romania -0.14 23.97 0.77 1463.33
26 France -0.13 26.12 0.82 4335.56
27 Lithuania -0.13 24.12 0.98 5461.96
28 Armenia -0.12 23.37 0.74 2039.46
29 Chile -0.1 24.54 0.96 5322.74
30 Argentina -0.1 26.39 0.99 8652.15