Thanks but this does not answer the question why infection rates were low before B.1.617 appeared, which is what I asked.
The mutations make it more transmissible. https://scholar.google.com/scholar?hl=en&as_sdt=0%2C6&q=B.1.617&btnG=#d=gs_qabs&u=%23p%3DzPBqQzAlNs0J
Thanks but this does not answer the question why infection rates were low before B.1.617 appeared, which is what I asked.
The mutations make it more transmissible. https://scholar.google.com/scholar?hl=en&as_sdt=0%2C6&q=B.1.617&btnG=#d=gs_qabs&u=%23p%3DzPBqQzAlNs0J