Viruses reproduce by taking over the replication machinery of host cells to make copies of their own genetic material, or genome. Unlike cellular organisms, whose genomes are made of DNA, viruses can encode their genomes as either DNA or RNA. Coronaviruses like SARS-CoV-2—the virus responsible for COVID-19—use RNA to store their genetic information, and copying RNA is more prone to mistakes than copying DNA. Researchers have shown that when a coronavirus replicates, around 3 percent of its copies contain a new random error, also known as a mutation.
A virus that is widely circulating in a population and causing many infections has more opportunities to replicate and thus to mutate. Most mutations are inconsequential glitches that do not affect how the virus works in a significant way. Others may even be detrimental to the virus. But a small fraction of the errors will prove advantageous to the virus, for example by making it more infectious.
As a virus mutates through the replication process, the resulting mutated version of the virus is called a variant. Public health agencies may give special labels to groups of variants that share a characteristic or attribute. These groups may contain variants that come from a single lineage, like an inherited trait in a family tree, or those that arise independently but behave similarly. In the case of SARS-CoV-2, variants are classified and labeled using letters of the Greek alphabet, e.g., the Delta and Omicron variants.
While it's not possible to stop viruses from mutating, health experts say it is possible to reduce the chances that a new and more deadly mutation will arise by limiting a virus's spread. In the case of SARS-CoV-2, health interventions like wearing masks, physical distancing, and vaccinations are important: They reduce the total number of times the virus can replicate and therefore the chances that it can develop a more dangerous mutation.
