In Zvi's last post, the comment thread includes data on the B.1.617, which seems to have cracked the contagiousness code in India. https://www.lesswrong.com/posts/4PTstS4Kt5hBMJTRL/covid-4-22-crisis-in-india?commentId=KQmoQRgHa2Qd2gJiz
Thanks but this does not answer the question why infection rates were low before B.1.617 appeared, which is what I asked.
I don't know if this is a complete answer, but maybe it has something to do with the average age?
India's population pyramid looks a lot different from the US or Europe:
Masks probably work well for less contagious variants and other respiratory diseases such as influenza, but after a certain threshold of contagiousness is reached, they don't.
This is why elastomeric respirators should be used during pandemics rather than masks.
The loosening of restrictions on gatherings might also be to blame.
https://www.nytimes.com/2021/04/20/opinion/india-covid-crisis.html
When I look at the numbers of Covid-19 cases and Covid-19 deaths among G20 countries, India still has a relatively low number per capita. The arguments for why the current wave is particularly catastrophical in India (like population density or poverty) applied all the time, however, except for the mutation. How did India manage to have relatively low case rates up to now?