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What’s the difference between a variant of interest and a variant of concern?

Variant of Interest - CDC
Photo via Raed Mansour/Flickr (CC BY 2.0)

To date, the World Health Organization has identified four COVID variants of concern: alpha, beta, gamma, and the highly transmissible delta. The international agency is also keeping track of several “variants of interest,” which include variants eta, iota, kappa, and lambda, along with 13 additional variants that have surfaced across the globe. With so many different strains out there, it can be confusing to differentiate between a variant of interest and a variant of concern.

The Centers for Disease Control and Prevention actually defines three variant classifications: variants of interest, variants of concern, and variants of high consequence. Fortunately, there have yet to be any COVID variants of high consequence identified in the United States.

A variant of interest typically constitutes “specific genetic markers that have been associated with changes to receptor binding.” These variants may result in reduced efficacy of treatments, potential increases in transmissibility, or higher severity of the disease. While variants of interest may be to blame for an increased number of regional cases or unique outbreak clusters, they have yet to spread to other countries.

Variants of concern embody the same attributes of a variant of interest, but can also be responsible for greater disease severity. They can additionally be responsible for increased hospitalizations or deaths, a “significant” drop in antibody response from a previous infection, and reduced effectiveness of treatment and vaccines. These strains likewise tend to be more highly transmissible. A mutation is elevated from a variant of interest to a variant of concern when evidence of the strain meets at least one of these criteria.

When the delta variant was designated a variant of concern in India, where it was first identified, the WHO and CDC were initially reluctant to label it as such. Dr. Gagandeep Kang, a virologist from the Royal Society of London, told the BBC back in June that data had yet to prove that delta was more infectious or led to more severe disease compared to other variants. 

“You need biological and clinical information in order to consider whether it is truly a variant of concern,” Kang said. “You need to study a few hundred patients who are sick with this condition and variant and find out whether they are at greater risk of greater disease than the ancestral variant.”

We now know how that ultimately turned out, as the delta variant is projected to kill 60,000 Americans by October.

It’s common for viruses to mutate. Typically, these changes are inconsequential. In some cases, mutations can even harm a virus. Other types of mutations, however, can cause a disease to become more infectious or threatening. When a mutation threatens to become a dominant strain, as is the case with delta, a variant of interest is elevated to one of concern.

Sources: CDC, Harvard, BBC, WebMD


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