This story originally appeared in WIRED Japan and has been translated from Japanese.
The Northern Hemisphere is entering another wave of COVID-19: While much of the world acts as if the pandemic is over, cases are rising again. The U.S. Centers for Disease Control and Prevention (CDC) registered an upturn in positive Covid tests, A&E visits, hospitalisations and deaths in recent weeks, while cases and hospital admissions in the UK They are sneaking up also.
But it is in Japan where the increase is particularly visible. The country’s National Institute of Infectious Diseases has… reported The average number of infected people per medical institution has been rising rapidly since June. In particular, Okinawa Prefecture has seen the highest number of new hospitalized patients since reporting began, and the virus may be spreading in Japan at a rate that exceeds the country’s last two major waves, in September 2023 and January 2024.
The culprits behind the surge are a new set of variants: KP.3, LB.1, and KP.2.3. Descendants of the JN.1 omicron sublineage that gained dominance over Christmas, they have emerged as the driver of new infections around the world, with KP.3 apparently gaining dominance. As of July 15, the U.S. CDC My dear About 37 percent of new Covid cases in the United States were due to KP.3, while KP.2 accounted for 24 percent and LB.1 for 15 percent. KP.3 has been rising rapidly in recent months: as of May 11, it accounted for about 9 percent of cases in the US; a month later, on June 11, its share was 25 percent.
Collectively, these viruses are called FLiRT variants, because they all have a mutation in the spike protein that changes its 456th amino acid from phenylalanine (F) to leucine (L) and its 346th amino acid from arginine (R) to threonine (T). According to a paper from the University of Tokyo’s Institute of Medical Sciences, published earlier this year in The Lancet Infectious Diseases journal, these variants are more transmissible than previous conventional variants and have a strong ability to evade neutralizing antibodies.
Genotype to Phenotype Japan (G2P-Japan), a research consortium of the institute, Dear All that the R numbers of the FLiRT variants (the average number of new cases caused by an infected person and a measure of infectivity) are higher for these new forms of the virus compared to JN.1. Furthermore, when these viruses were tested for infectivity in cultured cells, KP.3 required a smaller amount of virus to cause an infection compared to LB.1 and KP.2.3, which required roughly the same amount of virus as JN.1. These results provide a clue as to why KP.3 appears to be heading for dominance.
FLiRT variants, including KP.3, also outperform the ability of earlier forms of the virus to evade immunity. When the G2P-Japan team examined past infections, breakthrough infections (those occurring after vaccination), and neutralizing antibody responses induced by the updated COVID-19 vaccine XBB.1.5, they found that in all cases, neutralizing activity against FLiRT was significantly weaker than against existing epidemic variants.
