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 Moldova -0.15 25.07 1.2 7588.06
12 US -0.15 25.87 0.95 2789.58
13 Montenegro -0.13 28.51 1.13 9448.15
14 Croatia -0.13 21.75 1.17 1644.56
15 Panama -0.12 22.76 0.94 1820.12
16 Andorra -0.11 23.45 0.96 2431.56
17 Mexico -0.11 24.55 0.97 3069.28
18 Peru -0.11 24.69 0.93 5728.77
19 Portugal -0.11 26.4 0.72 1396.72
20 Spain -0.1 24.83 0.81 2612.92