The Covid-19 crisis has been caused by a new strain of coronavirus — a fairly common group of viruses and one of the main causes of the common cold. It was first reported to the World Health Organization (WHO) from China in December 2019. At the end of January 2020, the WHO declared the outbreak a public health emergency of international concern, and in March 2020 it declared a pandemic. A pandemic is the worldwide spread of a new disease, affecting millions of people and leading to a large number becoming ill.