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 | -0.45 | 35.4 | 0.99 | 5565.64 | |
| 2 | Bosnia and Herzegovina | -0.43 | 43.5 | 0.75 | 3462.22 | |
| 3 | North Macedonia | -0.39 | 39.94 | 0.63 | 2844.24 | |
| 4 | Moldova | -0.36 | 35.3 | 0.75 | 1659.69 | |
| 5 | San Marino | -0.36 | 42.19 | 0.14 | 126.28 | |
| 6 | Hungary | -0.35 | 48.14 | 0.73 | 4131.18 | |
| 7 | Montenegro | -0.34 | 39.58 | 0.79 | 2107.96 | |
| 8 | Bulgaria | -0.34 | 39.72 | 0.8 | 3694.15 | |
| 9 | United Kingdom | -0.33 | 30.28 | 0.96 | 723.64 | |
| 10 | US | -0.32 | 28.57 | 0.88 | 1906.65 |