I had heard this before but India is the largest vaccine country in the world.  Taken from an article from NPR:

Cyrus and Adar Poonawalla are the founder and CEO, respectively, of the Serum Institute of India. It's the world's largest vaccine-producing company in the world's largest vaccine-producing nation.

Here is the link if you want to read the full article:

https://www.npr.org/sections/goatsandsoda/2021/03/18/978065736/indias-role-in-covid-19-vaccine-production-is-getting-even-bigger