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 Belgium -0.42 34.74 0.96 5496.92
2 Bosnia and Herzegovina -0.38 41.74 0.99 9678.67
3 North Macedonia -0.33 37.12 0.83 7406.13
4 Moldova -0.31 34.46 0.84 3513.83
5 San Marino -0.31 43.06 0.66 2800.49
6 Hungary -0.3 46.13 0.76 10246.48
7 Bulgaria -0.3 38.49 0.81 8374.65
8 Montenegro -0.29 37.92 0.85 3343.25
9 United Kingdom -0.28 30.29 1.04 818.34
10 Slovenia -0.28 33.38 0.85 4544.86