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
11 Croatia -0.32 30.87 0.82 6882.94
12 Slovenia -0.32 33.97 1.02 4835.04
13 Liechtenstein -0.31 24.93 0.66 1994.32
14 Slovakia -0.31 35.14 0.86 1823.51
15 Mexico -0.3 27.7 0.84 1525.06
16 Italy -0.29 33.34 0.86 4034.78
17 Panama -0.29 23.78 1.02 1056.64
18 Portugal -0.28 26.06 0.83 517.28
19 Brazil -0.28 33.7 1.02 7195.57
20 Spain -0.28 26.62 0.82 2609.71