In the wake of this winter flu season, the holding of mass gathering, such as Kumbh Mela, may pose health risks. Maha Kumbh has been a case of study among health experts for a long time. Here's what studies and research have to say about health challenges at Maha Kumbh.

Maha Kumbh Mela or Great Pitcher Festival begins in India on Monday, a Hindu sacred event that will be the world's largest gathering of humanity as it showcases religion, spirituality, tourism and crowd management.

Vast crowds of Hindu pilgrims in India bathed in sacred waters as the Kumbh Mela festival opened on Monday, with organisers expecting 400 million people -- the world's largest gathering of humanity -- to assemble over six weeks.India is the world's most populous nation, with 1.4 billion people, and so is used to large crowds.