The number of cases of Covid-19 is increasing rapidly worldwide. Mostly, the number of cases – infected people confirmed by tests – is normalized by the population. However, the conditions of when a test is carried out on whom are very different in the countries. The number of undocumented cases is correspondingly different. The number of deaths, however, is comparable.

The typical mortality rate is used to conclude the undocumented number of infected people. This is very difficult to estimate. The distribution of the mortality rate from all countries provides information.

I have assumed that 1% of Covid 19 cases are fatal. The estimated cases, with undocumented numbers, for the 20 most affected countries look like this:

Obviously, also variations in the mortality rate will exits and this is certainly country specific. However, I consider these variations to be smaller than the undocumented number of infected people.

Herd immunity strategy has been pursued for a certain period in some countries (UK and Netherlands). To estimate that, I assumed that 99% of the unreported cases after surviving Covid-19 are immune to the virus.

Herd immunity only takes effect when 60% – 70% of the population has developed immunity. We are far from it in all countries. In Italy 1.5% of the people would be immune right now, but the health system there is already overloaded. Therefore, the only feasible way is to implement the prescribed restrictions and to protect yourself and your neighbours from infection.

Because immunity is so low, revocation of the restrictions would automatically trigger a new wave of infection, even if the infection rate was previously strongly suppressed by these restrictions. In the future, the restrictions will have to be fine-tuned to the infection rate until a vaccine or effective drug is on the market. Since an infected person can be contagious for up to 14 days, the restrictions can only be changed in these time ranges. We need this regulation in order to influence as little as possible in our personal and economic freedoms. We therefore need a long-term support program and a lot of patience.