For a "classic" seasonal flu [...], vaccinating 56% of the population would ensure complete and "efficient" protection of the population.
Some experts, through their science, have attempted to extend the concept of herd immunity to include immunity acquired, after recovery, by individuals infected with SARS-CoV-2. Contact with the infectious agent would thus play the same role as vaccination, by stimulating the immune defences against the pathogen. However, widespread contact can be disastrous. If the R0 is estimated to be 2.5 (between 1 and 3 under current assumptions) and if it is assumed that the contact is immunizing (e=1), then the x is of the order of 60%.