The XEC variant will likely become the world’s predominant SARS-CoV-2 variant in the near future, researchers from the Sato Lab, based at the University of Tokyo, reported recently in a preprint study.
XEC—first identified in Germany in early August—is a recombinant of two JN.1 descendant lineages, KS.1.1 and KP.3.3. In the United States, the KP.3.1.1 variant is still dominant and rising, making up an estimated 57.2% of SARS-CoV-2 viruses, the Centers for Disease Control and Prevention (CDC) said in its latest projections. However, it also noted a steady rise in XEC viruses, which make up about 10.7% of sequenced samples.
In comments on the study on X, Kei Sato, PhD, who leads the lab, said researchers compared the XEC variant with KP.3.1.1, finding that XEC has two spike mutations, compared to KP.3. The group’s phylogenetic epidemic dynamics modeling, based on surveillance from five countries, suggests that the reproduction number of XEC is greater than that of KP.3.1.1, which is currently the world’s dominant virus. The reproduction number is the average number of additional cases generated by each case in a susceptible population.
Increased infectivity, more immune-evasive
When the researchers examined virological properties with pseudovirus experiments, they found that the increase in infectivity was due to one of the two spike mutations (S:F59S) in XEC.
Experiments with XBB.1.5 and JN.1 sera to assess breakthrough infection found that neutralization titers for XEC and KP.3.1.1 were similar. However, compared to KP3.3 sera, neutralization against XEC was significantly lower than that of KP.3.1.1, and both mutations significantly increased resistance to KP.3.3 sera, suggestive of higher immune evasion.
Sato wrote that the higher reproduction number of XEC when compared to KP3.1.1 is partly attributed to the more robust resistance to KP.3.3.
