Increased receptor binding capability of the SARS-CoV-2 saltational variant PJ.2.1

The recently identified SARS-CoV-2 saltational variant PJ.2.1, a highly mutated descendant of MC.10.1, has achieved rapid intercontinental spread since its detection in May 2026. Here, we show that PJ.2.1 exhibits exceptionally high human ACE2-binding capability, significantly outperforming contemporary variants such as NB.1.8.1, XFG, and BA.3.2.2. However, despite acquiring over 25 spike mutations, PJ.2.1 remains antigenically similar to the circulating JN.1 family and does not display strong humoral immune evasion. Neutralization profiling indicates that PJ.2.1 possesses heightened neutralization sensitivity to human plasma and RBD-targeting antibodies, especially against cryptic-site-targeting class 4 and class 5 antibodies. This distinct sensitivity profile strongly suggests an altered spike structural dynamic that favors a receptor-accessible "up" conformation. While PJ.2.1 currently lacks the extreme immune evasion capabilities of other contemporary strains, its robust baseline receptor binding strength mirrors the early evolutionary trajectory of BA.2.86 to JN.1. This high receptor binding affinity provides a structural buffer that could facilitate the rapid acquisition of potent immune-evasive mutations, necessitating continued genomic, epidemiological, and virological surveillance of PJ.2.1.