I have a post where I analyze the idea that weather has an effect on the spread of coronavirus. One thing to note is that the best models focus on absolute humidity. This means that coastal Karachi is much better placed than inland Lahore, because Lahore often has low humidity. Mumbai shouldn’t be well suited for the spread of coronavirus at any time of the year (absolute humidity too high).
The major confound here: air conditioning. This creates a bubble of low absolute humidity, so coronavirus could spread very well in these environments. If you believe these results, one might want to turn off air conditioning in offices.