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The recent surge in COVID cases due to the Delta variant has created confusion and raised questions about how variants could change the global response to the coronavirus pandemic.

All viruses change over time, according to the World Health Organization. These different forms of a virus, a result of mutations, are called variants. Virus mutations can change the properties of viruses including how easily they spread, the severity of the disease they cause, or even the effectiveness of vaccines.

Since January 2020, WHO has been working with authorities and scientists around the world to monitor these variants in order to find the most effective pandemic response. Here are some of the variants on its radar.

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According to the CDC, there are three different categories for variants — Variants of Concern (VOC), Variants of Interest (VOI), and Variants of High Consequence (VOHC).

VOCs are variants for which there is evidence of increased transmissibility, more severe disease, or significant reduction in treatment or vaccine effectiveness. VOIs are variants that have a specific trait that has been associated with those characteristics.

The last category is VOHCs. These are variants with clear evidence that the effectiveness of prevention measures or medical countermeasures has reduced significantly. There are currently no variants that are labeled VOHC.

Variants of Concern (VOC)

According to the WHO, there are currently four variants labeled Variants of Concern — Alpha, Beta, Gamma, and Delta. According to the CDC, they are classified as “variants of concern” because there is evidence of changes in transmissibility, disease severity, or decrease in treatment effectiveness compared to the original virus.

Alpha

The Alpha variant was first detected in the United Kingdom in September 2020 and according to the CDC, is 50 percent more transmissible than earlier strains. The CDC also states that the Alpha variant has the potential to result in more severe cases based on hospitalization and case-fatality rates observed in people affected by the variant.

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Beta

First detected in South Africa in May 2020, the Beta variant also has a higher transmission rate than the original virus. According to the CDC, the Beta variant reduces the effectiveness of some monoclonal antibody treatments used in patients with COVID. Monoclonal antibodies are laboratory-made proteins that mimic the immune system’s ability to fight off harmful pathogens such as viruses.

Gamma

The Gamma variant was first detected in Brazil in November 2020. The Gamma variant has some of the same mutations in its spike protein as the Alpha and Beta strains, which allow it to attach more easily to human cells, making it more transmissible. Like the Beta variant, it also reduces the effectiveness of some monoclonal antibodies used to treat patients with COVID.

Delta

The Delta variant, which was first detected in India in October 2020, is the most contagious version of the virus so far and is much more easily contracted than previous strains. The Delta variant now represents more than 98 percent of COVID cases in the US, according to the CDC.

An internal CDC report which was obtained by The Washington Post, found that the Delta variant is more transmissible than the viruses that cause MERS, SARS, Ebola, the common cold, the seasonal flu, and smallpox, and is as contagious as chickenpox.

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In an environment with no vaccinations or mask-wearing, it is estimated that the average person infected with the original coronavirus strain will infect 2.5 other people. If infected with the Delta variant, the average person would infect up to 4 other people, according to one expert.

Variants of Interest (VOI)

Eta, Iota, Kappa, and Lambda have been labeled as Variants of Interest by WHO. Scientists classify these variants as “variants of interest” because they have characteristics that could potentially cause changes in transmissibility, disease severity, or a decrease in treatment effectiveness.

Eta

This variant of interest was first detected in December 2020 in the United Kingdom and Nigeria.

Iota

The Iota variant was first detected in New York in November 2020.

Kappa

The variant was first detected in India in October 2020.

Lambda

The Lambda variant was first detected in Peru in December 2020 and is now spreading rapidly through South America. A lab study in Japan, which has not yet been peer reviewed, found that the Lambda variant could be more resistant to vaccines than the original strain of COVID and could be highly infectious. Another non-peer reviewed study from NYU researchers found that vaccines generally worked well against this variant.

Mu

Mu was added to the Variants of Interest list on August 30, 2021. The variant was first detected in Colombia in January. During a virtual press event, WHO’s technical lead for COVID-19, Maria Van Kerkhove, said that while Mu’s mutations suggest it could evade the immune protection provided by natural infection or vaccination, the Delta variant is more concerning due to its transmissibility.

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Maria Elena Little Endara can be reached at mariaelena.littleendara@globe.com.