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
141 Nicaragua 75.72 0.44 1.02 6.78
142 Guinea-Bissau 100.06 0.56 1.05 20.98
143 Malawi 109.01 0.99 0.64 21.4
144 Singapore 125.9 1.08 1.03 22.21
145 Mozambique 116.52 0.44 0.78 18.03
146 Chad 147.71 0.18 1.19 17.77
147 Benin 149.81 0.14 1.46 22.98
148 Australia 160.09 0.57 1.46 16.39
149 Mauritius 239.75 0.21 0.19 5.06
150 Haiti 249.62 0.36 1.15 12.93