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 | -4.72 | 105.78 | 1.14 | 270.31 | |
| 2 | Brazil | -4.19 | 52.34 | 0.34 | 77.13 | |
| 3 | US | -3.85 | 54.15 | 0.84 | 915.32 | |
| 4 | United Kingdom | -3.63 | 51.93 | 1.08 | 682.09 | |
| 5 | Sweden | -3.47 | 36.61 | 1.14 | 121.03 | |
| 6 | Israel | -3.45 | 54.08 | 1.04 | 315.62 | |
| 7 | Singapore | -3.23 | 39.64 | 0.63 | 849.08 | |
| 8 | New Zealand | -3.16 | 46.03 | 1.11 | 1145.29 |