Is it worth getting the flu shot every year in India?

Yes, for most people, and the reason is that circulating influenza strains change each year, so last year's immunity does not carry over reliably. In India the seasonality is less clean than in temperate countries — there is a monsoon peak in much of the country and a winter peak in the north — so timing matters more than in the West. Pre-monsoon vaccination suits most regions. It is particularly worth it if you are over 60, pregnant, diabetic, asthmatic, or living with someone who is.