Yellow fever is transmitted by mosquito bite. It's not a major concern for people traveling in India, but it's important to know that when you get to India you may be asked to show proof of yellow fever vaccination if you visited a country with risk of yellow fever before your arrival in India.
Without that proof, you may be quarantined for up to six days when you first arrive. Yellow fever is mostly found in tropical and subtropical countries in Central America, South America, and Africa.