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News Navigator: What is the Delta coronavirus variant growing dominant worldwide?

The Delta coronavirus mutant strain is seen in this electron microscope photo provided by the National Institute of Infectious Diseases.

The Mainichi Shimbun answers some common questions readers may have about the Delta mutant strain of the coronavirus.

    Question: I hear the word "Delta variant" frequently in the news about COVID-19 these days, but what exactly is it?

    Answer: The Delta variant is one mutant strain of the coronavirus. It was first detected in India, and has an L452R mutation, in which the 452nd amino acid is replaced from leucine to arginine. There are three classes of the L452R mutation, but the Delta variant is the most dominant one. Incidentally, "Delta" comes from the letter of the Greek alphabet.

    Q: Why is the mutant strain named after a Greek letter?

    A: Coronavirus variants had previously been referred to using the name of the country where it was first found -- such as the "U.K. variant," or the "Indian variant." However, even if it was first detected in a certain country, this does not necessarily mean that the strain had undergone a mutation in the same country. Moreover, the World Health Organization raised the concern that calling coronavirus variants by country names may lead to stigma and discriminatory treatment and proposed in May to use new names with Greek letters.

    Q: What kind of mutant strains are there besides the Delta variant?

    A: Some examples are the Alpha variant, with an N501Y mutation, which was found in the United Kingdom and has also become dominant in Japan, the Beta variant first found in South Africa, and the Gamma variant which has spread in Brazil.

    Q: So what kind of characteristics does this dominant Delta variant have?

    A: It is believed that the Delta variant is even more infectious compared to the Alpha variant, which is said to be more transmissible than the conventional coronavirus strain. There have also been overseas analysis showing that those infected with the Delta variant are more prone to developing severe symptoms which require hospitalization than individuals who contract the Alpha variant. According to Japan's Ministry of Health, Labor and Welfare, a total of 224 people in 15 prefectures in the country had been confirmed infected with the Delta variant by June 28. The National Institute of Infectious Diseases has estimated that by mid-July, over 50% of COVID-19 patients in the greater Tokyo area will have been infected with the Delta variant.

    (Japanese original by Sooryeon Kim, Lifestyle and Medical News Department)

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