Conceptual illustration of four variants of the SARS-CoV-2 coronavirus, the cause of the Covid-19 pandemic. SARS-CoV-2 emerged in Wuhan, China, in December 2019 before spreading worldwide. Viruses are constantly changing through mutation. Some of the many new variants will persist in the population, while others will disappear. As of March 2021 there are three variants of the virus that are a cause for concern as they are either transmitted more easily or are able to evade parts of the immune response to infection.