Researchers from the University of Tokyo have indicated that the omicron subvariant JN.1, distinguished by the L455S "FLip" mutation in its spike protein, is on track to become the prevailing lineage of the SARS-CoV-2 virus worldwide. While the dominance of a strain does not inherently imply increased danger, experts emphasise that the nature of viruses involves constant mutations.

Designated as a separate variant of interest (VOI) on December 18, 2023, JN.1 originated from the BA.2.86 lineage, which surfaced in August 2023. This subvariant has rapidly gained prominence, surpassing its predecessor BA.2.86 and other omicron lineages, such as EG.5.1 and HK.3.

The FLip mutations, exemplified by L455S and L455F, switch amino acids F and L on the spike protein, enhancing transmissibility. A study published in The Lancet Infectious Diseases revealed that JN.1 swiftly became dominant in France, outpacing BA.2.86 and the FLip strains.

JN.1's transmissibility is reflected in its surpassing of HK.3 in France and Spain by the end of November 2023. The "FLip" mutations impact the receptor binding capacity of angiotensin-converting enzyme 2 (ACE2), a key protein facilitating the virus's entry into the body.

The University of Tokyo researchers, utilising a Bayesian multinomial logistic model, determined that JN.1's effective reproductive number (Re) is higher than other new variants like BA.2.86.1 and HK.3, indicating a growth advantage. This parameter is crucial for understanding the transmissibility of the virus in an epidemic.

While concerns have been raised about the potential evasion of vaccination by the JN.1 variant, INSACOG chief NK Arora has stated that there is currently no need for additional vaccine doses, except for specific vulnerable groups.

Globally, between November 20, 2023, and December 17, 2023, the World Health Organization reported a significant increase of 52 percent in new cases (850,000) and a decrease of 8 percent in new deaths (3,000). In the same period, India recorded 3,241 new cases and 21 deaths. The Southeast Asia Region reported over 9,200 new cases, reflecting a 388 percent increase.

However, experts caution that reported cases may not accurately represent infection rates due to reduced testing and changes in reporting mechanisms. The Centers for Disease Control and Prevention (CDC) in the United States notes that JN.1 is expected to account for 39-50 percent of all SARS-CoV-2 variants in the coming weeks, indicating a potential increase in transmissibility or immune evasion. The situation is being closely monitored globally, with the CDC acknowledging the continued growth of JN.1.

Despite the upsurge in JN.1, the EG.5 variant remains the most reported variant of interest (VOI) globally, although it has displayed declining trends in recent weeks.