July 23, 2024

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COVID-19 New Variant “JN.1” Spreads Rapidly in Japan

COVID-19 New Variant “JN.1” Spreads Rapidly in Japan

COVID-19 New Variant “JN.1” Spreads Rapidly in Japan

A new variant of the novel coronavirus, referred to as “JN.1,” is spreading in Japan. We consulted with Dr. Go, a local physician, regarding this development.

The reporter interviewed with Dr. Masanori Go who worked at Tokushima Red Cross Hospital.  He is a specialist in the Japanese Society of Anesthesiology, an ICLS course director for the Japanese Society of Emergency Medicine, and a JB-POT.

COVID-19 New Variant "JN.1" Spreads Rapidly in Japan

screenshot from yahoonewsjapan

What is the Mutant Virus “JN.1” of the Novel Coronavirus?

Editorial Team:
Please provide information about the new variant of the novel coronavirus known as “JN.1.”

Dr. Go:
JN.1 is a subtype of the Omicron strain, a mutation of the “BA.2” lineage that was prevalent domestically in 2022. Given its increasing detection rates worldwide, the World Health Organization (WHO) designated it as a Variant of Interest (VOI) in December 2023.

It has been on the rise in Japan since around November 2023. According to the Japan National Institute of Infectious Diseases, the detection rate of JN.1 was 11.6% for the week ending December 3, 2023, but it had surged to an estimated 31% by December 28, 2023. While there is a possibility that JN.1 has an enhanced ability to evade immunity, there are no reports suggesting an increased risk of hospitalization or severe outcomes.

JN.1 is also spreading internationally, with the Centers for Disease Control and Prevention (CDC) estimating that around 44% of new COVID-19 cases in the two weeks leading up to December 23, 2023, were caused by JN.1 in the United States. This marks a significant increase compared to the previous two weeks, indicating a rapid rise in detection rates. JN.1 has been detected in countries such as France, Singapore, the United Kingdom, and Sweden. As of December 16, 2023, WHO reports that 41 countries have reported this variant.

WHO suggests that with JN.1, there is an expectation of increased infections as we enter a full-fledged winter.

What is Current Situation of COVID-19 Infections?

Editorial Team:
While this article focuses on the introduction of the new mutant virus “JN.1,” please provide information about the current situation of COVID-19 infections.

Dr. Go:
Since May 2023, with the reclassification of COVID-19 under the Infectious Diseases Control Law to Category 5, reporting has shifted from comprehensive tracking to fixed-point surveillance based on reports from 5,000 medical institutions nationwide. According to this surveillance, there were 27,987 reported cases nationwide for the week of December 25–31, 2023, with an average of 5.79 cases per surveillance point. Hokkaido had the highest average at 12.28 cases per point, followed by Nagano at 10.65, and Aichi at 9.19.

How to Address the Spread of “JN.1” Infections?

Editorial Team:
Please provide insights into how the rapid increase in cases of the new mutant virus “JN.1” of the novel coronavirus is being addressed.

Dr. Go:
Considering the winter season, there is an anticipation that an exceptionally high number of infections will occur within this month. This is because, similar to the Omicron strain’s surge, not only is the percentage of infections increasing among existing cases, but the overall number of infections is also on the rise. While vaccination is believed to provide a certain level of control, it doesn’t guarantee complete prevention. Therefore, it is crucial to continue basic infection prevention measures such as hand hygiene and mask-wearing, just as before.


This news reveals the spread of the new variant of the novel coronavirus, “JN.1,” in Japan. With WHO designating it as a Variant of Interest, close attention is warranted for future developments.

COVID-19 New Variant “JN.1” Spreads Rapidly in Japan



(source:internet, reference only)

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