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 -0.32 31.7 1.0 4307.15
2 San Marino -0.21 38.36 1.23 15207.04
3 Bosnia and Herzegovina -0.2 24.84 0.76 2115.82
4 North Macedonia -0.18 25.1 1.26 5353.55
5 Bulgaria -0.17 24.77 1.23 7031.6
6 Slovenia -0.17 31.2 1.0 5169.81
7 Hungary -0.17 26.75 1.39 12496.3
8 Italy -0.16 27.49 1.2 7583.63
9 United Kingdom -0.16 30.43 0.77 2632.55
10 Liechtenstein -0.15 22.76 1.68 1625.99