Japan-led researchers alert about the JN.1 coronavirus variant’s heightened ability to evade the immune system.

In Tokyo, the swiftly spreading JN.1 coronavirus variant has been identified as more adept at evading the human immune system and exhibits increased infectiousness compared to earlier strains, according to researchers. This immune evasion, termed “immune escape,” renders the immune system less effective in responding to the infection. Kei Sato, a professor at the Institute of Medical Science, University of Tokyo, and other researchers warn that the newfound variant has the potential to evolve into an epidemic strain in the future.

The JN.1 variant, originating from the omicron BA.2 mutation that gained prominence in 2022, has been rapidly spreading globally since November 2023. Designated a “variant of interest (VOI)” by the World Health Organization (WHO) in December, the JN.1 variant has garnered attention due to its increasing prevalence.

According to Japan’s National Institute of Infectious Diseases, the proportion of JN.1 variant cases among COVID-19 patients surged from just over 10% in early December 2023 to slightly over 30% three weeks later, with indications of further significant increases. However, until recently, the detailed characteristics of this new strain remained unknown.

To shed light on JN.1’s properties, researchers utilized data from epidemiological studies involving viral genomes from the U.K., France, and Spain, employing cultured cells for their investigations. The findings revealed that JN.1’s “effective reproductive number,” representing how many individuals an infected patient can transmit the virus to, is approximately 1.2 to 1.4 times higher than that of the currently dominant strain.

Experiments conducted with cultured cells have indicated that the JN.1 variant may possess twice the infectiousness of the BA-2-86 omicron subvariant, commonly known as pirola, which gained global attention after its first appearance in Japan in the summer of 2023.

The immune evasion capabilities of the new JN.1 variant are reported to be 3.6 to 4.5 times higher than those of the pirola strain for antibodies generated in response to vaccination and 3.8 times higher for antibodies developed after a prior infection with the COVID-19 virus.

The research team expressed concern that JN.1 has the potential to spread globally and become the dominant strain in the ongoing pandemic. They emphasized the importance of implementing effective infection control measures.

These study findings were published in the sister journal of the British medical journal “The Lancet.”

(Japanese original by Ryo Watanabe, Lifestyle, Science & Environment News Department)