What to know
- Viruses like SARS-CoV-2 continuously evolve as changes in their genetic code (i.e., RNA nucleotide substitutions, insertions, deletions, and RNA recombination) occur during replication of the genome. 3
- SARS-CoV-2 has consistently changed since it first emerged in people, resulting in variants that are different from the first SARS-CoV-2 virus.
- Since its emergence in people, many variants of SARS-CoV-2 have evolved, and some have outcompeted previously circulating viruses in the United States and globally.
- Scientists use multiple classification systems to describe and communicate similarities and differences between SARS-CoV-2 viruses.
Overview
The U.S. Department of Health and Human Services (HHS) established a SARS-CoV-2 Interagency Group (SIG) to enhance coordination among:
- CDC
- National Institutes of Health (NIH)
- Food and Drug Administration (FDA)
- Biomedical Advanced Research and Development Authority (BARDA)
- Department of Defense (DoD).
This interagency group, which sits under the Public Health Emergency Countermeasures Enterprise (PHEMCE), identifies and characterizes emerging variants and assesses their potential impact on vaccines, therapeutics, and diagnostics.
The SIG meets regularly to evaluate SARS-CoV-2 variants and lineages circulating in the United States and to make recommendations about the classification of variants and lineages. A group of experts assesses the available data on variant/lineage proportions. They also assess how these changes may affect vaccines, therapeutics, and diagnostics, as well as transmission and severity of disease. Variants may be reclassified as more information becomes available.
The SIG has updated its classification system and working definitions for variants of SARS-CoV-2, the virus that causes COVID-19, to better reflect the current variant landscape. The previous system classified all Omicron sublineages as part of the Omicron VOC and therefore did not provide the distinction needed to compare new descendent lineages with altered phenotypic characteristics to the Omicron parent lineages (JN.1, KP.3). These classification updates allow for independent evaluation and tracking of Omicron sublineages and forthcoming new variants when required.
Similar to the WHO classification system, the SIG uses three types of classifications:
- Variant under monitoring (VUM)
- Variant of interest (VOI)
- Variant of concern (VOC)
Variant under monitoring (VUM)
A variant under monitoring is a SARS-CoV-2 variant with genetic changes that are suspected to affect virus characteristics and early signals of growth advantage relative to other circulating variants (e.g., growth advantage which can occur globally or in only one WHO region), but for which evidence of phenotypic or epidemiological impact remains unclear, requiring enhanced monitoring and reassessment pending new evidence.
If a variant has an unusually large number of mutations in known antigenic sites, but there are very few sequences and it is not possible to estimate its relative growth advantage, such a variant can be designated a VUM, if there is also evidence of community transmission* in ≥ 2 countries within a 2-4 week period.
* Evidence of community transmission could include that cases are not known to be travel related; there are no known transmission links between cases; variant is detected in wastewater, preferably at more than one sampling point; and/ or there is an upward trend.
Variant of interest (VOI)
A variant of interest is a SARS-CoV-2 variant with genetic changes that are predicted or known to affect virus characteristics such as transmissibility, virulence, antibody evasion, susceptibility to therapeutics and detectability
AND
has been identified to have a growth advantage over other circulating variants in more than one WHO region with increasing relative prevalence alongside increasing number of cases over time, or other apparent epidemiological impacts to suggest an emerging risk to global public health.
Variant of concern (VOC)
A variant of concern is a SARS-CoV-2 variant that meets the definition of a VOI (see above) and, through a risk assessment conducted by the SIG, and determined to be associated with a moderate or high level of confidence, meets at least one of the following criteria when compared with other variants:
- Detrimental change in clinical disease severity, OR
- Change in COVID-19 epidemiology causing substantial impact on the ability of health systems to provide care to patients with COVID-19 or other illnesses and therefore requiring major public health interventions, OR
- Significant decrease in the effectiveness of available vaccines in protecting against severe disease.