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
131 Algeria 32.02 1.2 1.16 80.28
132 Angola 32.38 0.31 1.1 80.91
133 Togo 37.15 0.28 0.78 75.37
134 Zambia 36.43 1.15 0.88 63.65
135 Senegal 39.39 1.11 0.95 69.26
136 Mauritania 38.71 1.64 1.08 62.39
137 Rwanda 43.72 0.44 0.59 47.94
138 Sri Lanka 42.37 0.47 1.01 63.15
139 Uzbekistan 59.52 0.31 1.31 49.71
140 Guinea 75.69 0.19 0.83 28.13