Herd immunity for COVID-19 could be lower than thought
Basic models for COVID-19 suggest herd immunity is achieved when 60% of people are immune.
This is because in a population where everyone is susceptible to coronavirus, an infected person is estimated to infect on average an additional 2.5 people.
Yet if 60% of those theoretical 2.5 people are immune, then only one new infection can take place, and the outbreak cannot grow.
This is based on a very simple model,