@MountainJay @Johncdvorak
Generally speaking, from my knowledge, the correct definition of "herd immunity" is the one on the left screenshot. Problem is, with most infectious diseases, Covid-19 included, it's actually borderline impossible to achieve herd immunity only through normal infections, without a vaccine (you need 70-90% of population to become immune, which by natural means alone would take far too long to accomplish). Practically speaking, you won't be able to achieve herd immunity without a vaccine, which is why it's a concept worth discussion only in regards to how much of the population got vaccinated.