Covid-19: Does Sweden have herd immunity?

UPDATE 14th November 2020: In light of the recent increase in hospitalizations and deaths during October and November in Sweden, I no longer believe that Sweden reached a state of herd immunity during spring. The text below represents my thinking on the 19th of September, when I wrote the article, and doesn’t represent my current thinking. It is clear that a significant level of population immunity did build up during spring and summer, since the rise in hospitalizations has been much slower during the autumn than it was during the spring, and also seems to be stabilizing at a much lower level. However, the level of population immunity is clearly not as high as I previously thought. The reason I made this mistake is that the early evidence on covid suggested that it was not behaving in a seasonal manner. This caused me to underestimate the seasonal effect of summer to push down infections, which caused me to overestimate the level of population immunity that had built up during spring. It is now clear that covid is a highly seasonal virus. read more