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
1 Peru -0.89 95.92 0.98 6236.32
2 Bosnia and Herzegovina -0.56 45.62 0.82 264.02
3 North Macedonia -0.52 41.25 0.7 121.57
4 Belgium -0.51 34.9 0.9 804.04
5 Moldova -0.48 35.84 1.05 317.21
6 Montenegro -0.47 40.57 0.9 326.59
7 San Marino -0.47 41.48 5.0 0.0
8 Hungary -0.46 48.16 0.79 233.09
9 United Kingdom -0.45 30.87 1.22 3223.63
10 Bulgaria -0.45 40.35 0.81 398.17