Viruses mutate over time, and as a result, new variants of viruses tend to emerge. Most mutations do not produce clinically relevant changes but occasionally mutations occur that may be beneficial for the virus.
Multiple variants of SARS-CoV-2, the virus that causes COVID-19, have emerged in different parts of the world, and several of these have been documented in the United States. Some of these variants appear to be associated with increased transmissibility, but to date there is no evidence these variants cause more severe disease than the original strain of SARS-CoV-2 that emerged in Wuhan in 2019, nor is there evidence they are associated with reduced vaccine efficacy or a reduced response to SARS-CoV-2 monoclonal antibody therapies.
For timely information on emerging variants and vaccine efficacy, read our COVID-19 Vaccine FAQ on SARS-CoV-2 Variants.