Variants of Concern Vs Variants of Interest—as Omicron Spreads, What's the Difference?

On Friday, the World Health Organization (WHO) met to discuss a new COVID variant named B.1.1.529, which was first identified in southern Africa. The WHO named it Omicron, and labeled it a variant of concern.

The WHO tracks new COVID variants and their properties, such as how easily they spread, how severely infected people fall ill, and how effective vaccines and other measures are in curtailing their spread.

To assist in the tracking of variants and informing the general public and authorities about these variants, both the WHO and the U.S. Centers for Disease Control (CDC) and Prevention have different classifications for variants.

These categories range in severity and risk from the lowest risk category, Variants of Interest (VOI), to Variant of Concern (VOC). There is also another category in the CDC's classification scheme reserved for the most dangerous variants: Variants of High Consequence (VOHC).

For a variant to be designated a VOC by the WHO, it must meet criteria for a Variant of Interest, and also have one or more of the following changes at a degree that is significant to global public health. The variant must show an "increase in transmissibility or detrimental change in COVID-19 epidemiology," an "increase in virulence or change in clinical disease presentation," or a "decrease in effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics."

Omicron is not yet known to be in the U.S., and the CDC has not yet classified it as a VOC. However, according to the CDC's definition a VOC shows: "evidence of an increase in transmissibility, more severe disease (e.g., 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."

Though we currently know little about Omicron, its status as a VOC arises from the fact that it is a highly mutated version of COVID, according to the WHO. Of the fifty mutations observed in the Omicron variant, around 30 are found in the spike protein that helps the virus bind to human cells.

This means that the virus could be more efficient at reinfecting people who have already had COVID and it could also help it slip through the immunity conferred by vaccination.

This meets two criteria for a variant of concern as defined by the CDC: "Evidence of significant decreased neutralization by antibodies generated during previous infection or vaccination" and "Evidence of reduced vaccine-induced protection from severe disease."

There is also currently limited evidence of Omicron meeting another CDC criteria for a VOC, as it seems to demonstrate an increased level of transmissibility.

Other VOCs as defined by WHO are Delta—still responsible for the vast majority of current COVID infections—Alpha, Beta, and Gamma.

What is a Variant of Interest?

The WHO defines a VOI as a variant "with genetic changes that are predicted or known to affect virus characteristics such as transmissibility, disease severity, immune escape, diagnostic or therapeutic escape" or a variant that has been found to cause significant community transmission and other impacts that could suggest an emerging risk to global public health. The CDC has a similar definition.

Current VOIs identified by WHO are Lambda and Mu, with the Eta, Iota, and Kappa variants having dropped out of this category after the risk they posed reduced.

This means that if the mutations of the Omicron variant prove to be less adept at dodging antibody response provided by previous infection or vaccination than previously thought, it could drop from a VOC to a VOI. But, in the worst-case scenario that the Omicron variant proves to be even riskier that thought, it could rise into the as of yet unoccupied VOHC category.

The CDC says this classification is reserved for COVID variants that demonstrate the failure of diagnostic tests, show evidence to suggest a significant reduction in vaccine effectiveness and a disproportionately high number of infections in vaccinated persons, or result in a very low vaccine-induced protection against severe disease.

VOHCs could also demonstrate significantly reduced susceptibility to multiple Emergency Use Authorization therapeutics or other treatments, as well as presenting more severe clinical disease and increased hospitalizations.

COVID variants
A stock image of a hospital ward where patients are treated for COVID infections. The newly identified variant Omicron has been identified as a variant of concern. gorodenkoff/GETTY