SARS-CoV-2 Variant Classifications and Definitions

A VOHC has clear evidence that prevention measures or medical countermeasures (MCMs) have significantly reduced effectiveness relative to previously circulating variants. CDC monitors all variants circulating in the United States. In addition to the possible attributes of a variant of concern, variants designated as VOHC include impact on MCMs such as:

• demonstrated failure of diagnostic test targets.
• evidence to suggest a significant reduction in vaccine effectiveness, a disproportionately high number of infections in vaccinated persons, or very low vaccine-induced protection against severe disease.
• significantly reduced susceptibility to multiple EUA or approved therapeutics.
• more severe clinical disease and increased hospitalizations.

A variant of high consequence would require notification to WHO under the International Health Regulations, reporting to CDC, an announcement of strategies to prevent or contain transmission, and recommendations to update treatments and vaccines.

Currently, no SARS-CoV-2 variants are designated as VOHC. Classifications may change over time, based on the information available.

CDC monitors all variants circulating in the United States. In addition to the possible attributes of a variant of interest, variants designated as VOC include:

• increase in transmissibility.
• more severe disease (for example, increased hospitalizations or deaths).
• significant reduction in neutralization by antibodies generated during previous infection or vaccination.
• reduced effectiveness of treatments or vaccines, or diagnostic detection failures.

Variants of concern might require one or more appropriate public health actions such as:

• notify WHO under the International Health Regulations.
• report to CDC, local or regional efforts.
• increase preventative measures, such as masking, testing or physical distancing.
• conduct research to determine the effectiveness of vaccines and treatments against the variant.

Diagnostic tests, vaccines or treatments may be adapted to increase efficacy against circulating variants of concern.

Currently, no SARS-CoV-2 variants are designated as VOC. Classifications may change over time, based on the information available.

CDC monitors all variants circulating in the United States. Variants designated as VOI include variants that have:

• reduced neutralization by antibodies generated against previous infection or vaccination.
• reduced efficacy of FDA approved treatments, or diagnostic tests.
• predicted increase in transmissibility or disease severity.

Possible attributes of a Variant of Interest include:

• specific genetic markers that are predicted to affect transmission, diagnostics, therapeutics, or immune escape.
• evidence that it is the cause of an increased proportion of cases or unique outbreak clusters.

A Variant of Interest may have limited prevalence in the United States, but potentially expanding in other countries. It might require one or more public health actions. CDC may increase surveillance or epidemiologic investigations to evaluate the risk a VOI may have on the United States.

CDC monitors all variants circulating in the United States. Variants designated as VBM include:

• lineages with potential impact on available medical countermeasures based on analysis of genetic sequence data.
• lineages that previously caused more severe disease or increased transmission but that are no longer detected.
• lineage with an unusually large number of antigenic mutations AND presence in multiple countries with collection dates within 4 weeks.
• lineages previously designated as a VOI, VOC, or VOHC that are currently circulating at very low levels in the United States.

A Variant of Interest or a Variant of Concern may be downgraded to this list after it is no longer circulating at sustained levels and no longer poses significant risk to public health in the United States. Classifications may change over time, based on the evolving situation and information available.

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*Non-peer-reviewed