WHO and US-CDC Announce New Threat Levels for Coronavirus Variants

Just as stricter social distancing measures and vaccination were thought to be calming the COVID-19 Pandemic, reports from various countries of more transmissible coronavirus variants caused concern. Some reports even suggest that these variants are more deadly. The US Centers for Disease Control and Prevention (US-CDC) and the World Health Organization (WHO) therefore established new criteria for classifying variants of SARS-CoV-2, the virus that causes COVID-19.

The criteria below provide explanatory information about recent mutations / changes in circulating viruses. The levels also help people understand and communicate risk.

Types of Coronavirus Variants

The new designations are "variant of interest," "variant of concern," and "variant of high consequence." 

• A variant of interest has caused distinct clusters of infections in the United States or other countries, or appears to be causing an increase in cases. It also has genetic changes suggesting it may be more transmissible or better able to evade immunity from natural infection or vaccination. Therapeutic agents and tests may also work less well against it. The CDC is monitoring three of these.
• A  variant of concern has been shown through scientific studies to be more transmissible or cause more severe disease. It may also reduce the effectiveness of agents tested as treatments and of vaccines. People who previously had COVID-19 may be reinfected with this new variant. The CDC is following five of these.
• A  variant of high consequence causes more severe disease and more hospitalizations. It has also been shown to overcome medical countermeasures such as vaccines, antiviral drugs, and monoclonal antibodies. So far, no variant meets this definition.

The CDC said it casts a wide net when tracking the new criteria and identifying variants of interest, but would need stronger evidence before calling a variant one of concern.

According to a CDC spokesperson, "The CDC is aligned with the WHO approach in that the threshold for identifying a variant of interest should be relatively low to monitor potentially important variants with the greatest public health implications; however, the threshold for identifying a variant of concern should be high"

Previously, the CDC classified variants, but this is about to change somewhat. In future, the CDC will make final decisions on which variants warrant attention in consultation with a new SARS Interagency Group on variants, consisting of experts from the US National Institutes of Health (US-NIH), the US Food and Drug Administration (FDA), the Department of Defense, the Biomedical Advanced Research and Development Authority, and the Department of Agriculture.

How Are Variants Monitored?

Beyond the new CDC / WHO designations, Public Health England, the UK counterpart to the CDC, uses an additional classification for "variants under investigation." Variants under investigation have been newly identified and are the subject of ongoing studies, but scientists still know very little about their public health significance.

On Tuesday, 16 March, Public Health England announced that it was investigating the emerging P3 variant first detected in the Philippines.

On Monday, researchers in Colombia described a new variant of B.1.111 with spike protein mutations at L249S and E484K in a preprint study that they published. These two mutations have been found to help other viruses evade antibodies produced by the body in response to both vaccination and natural infection.

Public Health France also announced on Tuesday a new cluster of cases caused by a new variant in the 20C clade linked to a hospital in Brittany. The French variant has nine mutations in its spike protein and was not detected by PCR testing, suggesting that the changes prevent detection with these tests.

How Should Variants Be Viewed?

When a virus mutates or acquires a change in its genetic code, this creates a variant. It is simply a version of the virus that differs from the one that produced it. Variants emerge frequently and are generally not harmful to humans. Sometimes, a change or set of changes helps one version outcompete other variants, and that variant or variants become dominant worldwide. For example, it may replicate faster or develop a different or more effective way to infect cells. Sometimes a change alters its structure enough that antibodies made by our immune system cannot attach to it.

When this happens, more illness and more severe disease may follow. Drug companies may need to modify drugs and vaccines to keep pace.

Points of Concern

So far, the CDC is tracking five variants of concern:

• First identified in the United Kingdom, the B.1.1.7 variant;
• Detected in Japan and Brazil, the P.1 variant;
• Reported in South Africa, the B.1.351 variant; and
• Spreading in California, the B.1.427 and B.1.429 variants. 

Surveillance of these variants is currently limited. The United States performs relatively little genomic surveillance of the virus compared with other countries such as the United Kingdom.

The B.1.1.7 variant is at least 50% more transmissible than older versions of the virus. It caused major COVID-19 surges in the United Kingdom, Israel, and Europe. The CDC says that, as of 16 March, 4686 cases had been detected in the United States, spanning all 50 states.

Laboratories have detected 142 cases of the B.1.351 variant, coming from 25 US states. There have been at least 27 cases of the P.1 variant in at least 12 states. Studies have shown that existing vaccines are less effective against these two variants. They are also not susceptible to some monoclonal antibody therapies under development. Like B.1.1.7, B.1.351 appears approximately 50% more transmissible.

The B.1.427 and B.1.429 variants appear approximately 20% more transmissible than earlier versions of the virus. They may also slightly reduce the effectiveness of vaccines and therapeutics. Vaccine-produced immunity is so strong that this reduction is not expected to prevent them from being effective at preventing infections or reducing viral transmission.

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