Novel Coronavirus (SARS-CoV-2), the virus that causes COVID-19 disease among humans has evolved and mutated multiple times since it was first reported in China's Wuhan in December, 2019. A mutation is a change in the genome or genetic sequence of a virus which results in a new strain of the virus. Here are five quick facts about the Delta variant of COVID-19 which has been declared as a variant of concern by World Health Organisation (WHO).