Find Data from the Wisconsin State Laboratory of Hygiene Show A variant is a new strain of the SARS-CoV-2 virus, the virus that causes COVID-19. Variants occur through mutations, which are changes in the genetic code of a virus. Variants have specific gene mutations that make them unique and different from the original virus. Viruses, including SARS-CoV-2, naturally change or mutate over time and new variants are expected to occur. Variants are identified through a process called whole genome sequencing. Whole genome sequencing takes a sample of the virus from a positive SARS-CoV-2 test specimen and reads its genetic code. Genomic sequencing allows scientists to identify how virus samples from different people might have different genetic characteristics. This way, they can look out for new variants of the virus and better understand how different mutations change the characteristics of the virus, like how easily it spreads from person-to-person. The Department of Health Services (DHS), the Wisconsin State Laboratory of Hygiene, and other laboratory partners regularly perform whole genome sequencing on a portion of positive tests. DHS has also requested that clinicians identify cases that may be good candidates for genome sequencing, such as individuals who have traveled internationally or individuals who may have tested positive after being up to date with COVID-19 vaccines. Why track SARS-CoV-2 variants?
The CDC classifies variants into four categories:
A variant's classification is based on its attributes, including:
The classification of a particular variant might change based on new research. Learn more about SARS-CoV-2 variant classifications on the CDC website.
Visit the CDC website for more information on the Omicron variant.
Visit the CDC website for more information on the Delta variant. All viruses mutate, or change, over time. Mutation can happen very slowly or more quickly. The longer a virus sticks around, the more time it has to change. When a virus changes, it is called a variant. Many variants are no more harmful than the original virus, however, some can be more infectious or deadly. When our bodies are faced with a new variant, our immune responses built from vaccination or a previous infection may be able to fight it off. Vaccines reduce a virus's ability to infect people. Vaccines still provide protection against current variants since many of the characteristics of the virus remain the same. The sooner people get vaccinated against COVID-19, the less opportunity we give the virus to keep mutating.
 Available in Spanish.
Available in Spanish. Last Revised: May 27, 2022
ECDC regularly assesses new evidence on variants detected through epidemic intelligence, rules-based genomic variant screening, or other scientific sources. If a decision is made to add, remove, or change the category for any variant, the tables are updated to reflect this change. The tables are regularly sent for consultation to ECDC and WHO Regional Office for Europe’s joint virus characterisation working group. The rules-based genomic screening is performed using an open source algorithm. The weekly ECDC variant surveillance data report can be found in the weekly COVID-19 country overviews published on ECDC’s website. More information on variants is available on The tables include: Category: variant of concern (VOC), variant of interest (VOI), or variant under monitoring (VUM) (see definition above each table). Note that it is a possible for a VOC, VOI or VUM to also be a part of a broader VOC, VOI, or VUM definition, e.g. B.1.617.2+E484X is also a part of B.1.617.2, this means that there is enough evidence to fulfil the VOC, VOI or VUM criteria for this variant using the broader variant as a reference. For these variants, clear evidence is available indicating a significant impact on transmissibility, severity and/or immunity that is likely to have an impact on the epidemiological situation in the EU/EEA. The combined genomic, epidemiological, and in-vitro evidence for these properties invokes at least moderate confidence. In addition, all the criteria for variants of interest and under monitoring outlined below apply.
x: A67V, Δ69-70, T95I, G142D, Δ143-145, N211I, Δ212, ins215EPE, G339D, S371L, S373P, S375F, K417N, N440K, G446S, S477N, T478K, E484A, Q493R, G496S, Q498R, N501Y, Y505H, T547K, D614G, H655Y, N679K, P681H, N764K, D796Y, N856K, Q954H, N969K, L981F y: G142D, N211I, Δ212, V213G, G339D, S371F, S373P, S375F, T376A, D405N, R408S, K417N, N440K, S477N, T478K, E484A, Q493R, Q498R, N501Y, Y505H, D614G, H655Y, N679K, P681H, N764K, D796Y, Q954H, N969K All sub-lineages of the listed lineages are also included in the variant, e.g., BA.1.1 is included in Omicron BA.1 as it is a sub-lineage of BA.1. Variants of Interest (VOI)For these variants, evidence is available on genomic properties, epidemiological evidence or in-vitro evidence that could imply a significant impact on transmissibility, severity and/or immunity, realistically having an impact on the epidemiological situation in the EU/EEA. However, the evidence is still preliminary or is associated with major uncertainty. In addition, all the criteria for variants under monitoring outlined below apply.
x: Any amino-acid substitution Variants under monitoringThese additional variants of SARS-CoV-2 have been detected as signals through epidemic intelligence, rules-based genomic variant screening, or preliminary scientific evidence. There is some indication that they could have properties similar to those of a VOC, but the evidence is weak or has not yet been assessed by ECDC. Variants listed here must be present in at least one outbreak, detected in a community within the EU/EEA, or there must be evidence that there is community transmission of the variant elsewhere in the world.
z: A67V, Δ69-70, Δ143-145, N211I, Δ212, G339D, S371F, S373P, S375F, D405N, K417N, N440K, G446S, S477N, T478K, E484A, Q493R, Q498R, N501Y, Y505H, D614G, H655Y, N679K, P681H, D796Y, Q954H, N969K n/a: not applicable, no WHO label has been assigned to this variant at this time De-escalated variantsThese additional variants of SARS-CoV-2 have been de-escalated based on at least one the following criteria: (1) the variant is no longer circulating, (2) the variant has been circulating for a long time without any impact on the overall epidemiological situation, (3) scientific evidence demonstrates that the variant is not associated with any concerning properties.
n/a: not applicable, no WHO label has been assigned to this variant at this time All sub-lineages of the listed lineages are also included in the variant, e.g., B.1.429.1 is included in B.1.427/B.1.429 as it is a sub-lineage of B.1.429. (a) No assessment of transmission is given for variants in the monitoring category, only detected/not detected. (b) The earliest detections from several different countries are close in time and there is no clearly demonstrated travel link to a specific country that explains the detections. (c) The property of concern for this variant was the fact that there are reports of difficulties associated with detecting it in upper respiratory tract samples. These difficulties were not caused by primer-template mismatch but rather by the virus not being present in sufficient quantities in the upper respiratory tract. (d) Any amino acid substitution See changes from previous weeks Geographic scope of the tablesThe tables are based on genomic, phenotypic, and epidemiological evidence available on a global scale, but focus on the potential impact for the European region. For this reason, the list may deviate slightly from the global variants of concern and interest list and labels produced by WHO and published in the WHO weekly epidemiological update.
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