This article is part of a series of explainers on vaccine development and distribution. Learn more about vaccines – from how they work and how they’re made to ensuring safety and equitable access – in WHO’s Vaccines Explained series.All viruses – including SARS-CoV-2, the virus that causes COVID-19 – evolve over time.
When a virus replicates or makes copies of itself, it sometimes changes a little bit, which is normal for a virus. These changes are called “mutations”.
A virus with one or more new mutations is referred to as a “variant” of the original virus.What causes a virus to change to a new variant?When a virus is widely circulating in a population and causing many infections, the likelihood of the virus mutating increases.