Essentially they're concerned if you've come from a Yellow Fever area, and should have both the book + stamp to prove vaccination, and of course have had the vaccination. Of course if you've not been to those countries, then it's not as important. They recommend not getting the Yellow Fever vaccination for India.
The other concern is Malaria. Below 2000m it exists throughout the country. Unfortunately there's no vaccination, and some strains are even resistant to some drugs. You'll need to look at what area you're going to, and then find out if it's worth getting a drug to take while in that area (they're simple tablets). Your GP or travel doctor can advise.
Personally if there's a risk of Malaria, I take the pills. They're cheap, don't seem to give me side effects, and I've seen people who have had Malaria and would rather not take that risk.