It's a long flight and at 5 months, it's a crapshoot with regards to how your child will behave. A little younger, and it would be easier, but I would still go, with a few caveats.
We flew to California with our 5 month old this Christmas...he was awesome on the way out there, a nightmare on the way back. We were delayed 4 hours on the way back, so it was a LONG travel day and he just couldn't handle it by the time we were finally under way.
If you plan to go, I highly recommend get a ticket you can cancel. If your dc has an ear infection or you've been fighting off daycare colds/sickeness/etc. I wouldn't go. It's the middle of flu season too, so there's that to consider.
If you do end up going, I recommend wearing baby in a sling during the flight...the only way you'll be comfortable in today's coach class, or even better, buy a seat for DC's carseat.
As for vaccinations, I believe you don't need anything exotic to go to India. I would consult with a pediatrician in advance, most definitely.