Covid-19 protection: Herd immunity vs vaccines – what will work? Wall Street Journal

In March, it was speculated that if the epidemic runs largely unchecked in South Africa through winter – the great majority of younger and healthy people would get the virus, develop only mild symptoms, and recover. They would thereby attain a degree of immunity which would, in aggregate, provide herd immunity to the broader society. This would have the potential to bring a sustainable end to the pandemic in South Africa. The concept of herd immunity has been put to the test in Sweden, which has had relaxed approach to the coronavirus outbreak. While the rest of the world was imposing national lockdowns, Sweden chose not to. Herd immunity means that enough people in a population have become immune to the virus — either through vaccine or previous infection — that the risk of new infections lowers across the board. In other words, the idea was, if Sweden kept its bars and restaurants open, more people among the less vulnerable would develop immunity and ultimately slow the spread. At first, Sweden's controversial approach appeared to be working. However, the country's eventual death toll, which greatly exceeds that of its Nordic neighbours, means Sweden has provided a cautionary tale. – Nadya Swart

What it would take to reach herd immunity 

We know that Covid19 spreads through close contact, making crowded areas potentially deadly. But when some members of a crowd are immune, that begins to change. This is called herd immunity. It's what's protecting much of the population from diseases like measles and polio, and it's what's driving vaccine efforts today. 

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