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 | -1.14 | 98.1 | 1.03 | 1956.68 | |
| 2 | US | -0.68 | 34.63 | 0.87 | 5051.42 | |
| 3 | Brazil | -0.64 | 45.15 | 1.21 | 2672.86 | |
| 4 | United Kingdom | -0.41 | 34.3 | 1.08 | 7124.12 | |
| 5 | Sweden | -0.39 | 23.08 | 0.68 | 797.9 | |
| 6 | Israel | 0.17 | 14.85 | 0.83 | 3815.71 | |
| 7 | Singapore | 2.71 | 1.47 | 1.45 | 1058.42 | |
| 8 | Australia | 3.28 | 0.81 | 1.28 | 852.04 | |
| 9 | New Zealand | 132.03 | 0.1 | 0.93 | 18.87 |