While the Kumbh Mela festival is ordinarly held every three years, rotating between several holy cities on the banks of these rivers, the Maha Kumbh Mela occurs only once every 12 years. Maha means “great”, and the event attracts the most devotees because it is considered the most auspicious and holy in the cycle.

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.

Hindu devotees from across India flocked to the northern city of Prayagraj yesterday as the world's largest religious festival began. Over the coming 45 days, an estimated 400 million Hindus are expected to come together for Maha Kumbh Mela.