You raise interesting points about herd immunity, though the statistics cited in the article about India are a bit puzzling, given its population of about 1.3 billion. So far there have been about 31 million confirmed cases there and around 500,000 deaths. Also, no one actually knows what the percentage of the population anywhere that will need to become immune one way or the other and the 70% figure is an educated guess. Here's some info:
The percentage of people who need to be immune in order to achieve herd immunity varies with each disease. For example, herd immunity against measles requires about 95% of a population to be vaccinated. The remaining 5% will be protected by the fact that measles will not spread among those who are vaccinated. For polio, the threshold is about 80%. The proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known. This is an important area of research and will likely vary according to the community, the vaccine, the populations prioritized for vaccination, and other factors. |
