Many people have accepted the anti-covid vaccination to protect their loved ones and contribute to herd immunity. But what do we really mean by “herd immunity”? ? This expression can be understood as the sum of the individual immunities. As a matter of fact, it designates a theory based on a mathematical model which claims to put into equation the phenomenon of contagion. This model justifies freedom-killing vaccination obligations in the name of “societal altruism”… As we will find out, herd immunity theory, real reason of state, has never proven its validity.