What is herd immunity, how to calculate, and at what price?
Herd immunity depends on the rate of transmission of COVID-19 in a country. If we take R0 of 2.5, it will need 60% of the population to be infected before getting herd immunity. It will have a price in mortality. Considering UK population, getting herd immunity will come with deaths of about 400,000 people.
Further reading
https://towardsdatascience.com/a-data-science-view-of-herd-immunity-what-do-we-have-to-pay-to-stop-the-virus-3a05fc2ce720
Interesting article in towardsdatascience.com above.
One more thing, which I did not see when quickly going through that article, is that even if the virus does not mutate, it is my understanding that we cannot assume at this point that surviving this particular virus will mean you will stay immune to it. That, as well as mutation, which was mentioned, would cause these equations to underestimate the problem.
After the today's announcement of WHO which asked everyone to be ready to live with COVID-19, It seems like coronavirus should be able to attack the world in the same way that common flu virus does.
More skepticism, less clarity about immunity after COVID-19
Read of this latest article on the topic:
Article COVID-19 and Postinfection Immunity: Limited Evidence, Many ...
It is not easy to say the population of the world that will be affected before the development of HERD IMMUNITY. The world is about 7.3 billion people. I believe that before the end of the year 2020, the vaccines should be available. Again, by then a lot of people must have adapted environmentally, economically, psychologically, and socially to cope with the COVID-19.
According to the latest publication as linked below, even repeated infections may not lead to immunity to COVID-19.
https://www.medrxiv.org/content/10.1101/2020.06.13.20130252v1.full.pdf