https://pubmed.ncbi.nlm.nih.gov/38782005/
The JN.1 variant (BA.2.86.1.1), arising
from BA.2.86.1 with the S:L455S substitution, showed increased fitness
and outcompeted the previous dominant XBB lineage by the beginning of
2024.
JN.1 subsequently diversified, leading to the emergence of descendants
with spike (S) protein substitutions such as S:R346T and S:F456L.
Particularly, the KP.2 (JN.1.11.1.2) variant, a descendant of JN.1
bearing both S:R346T and S:F456L, is rapidly spreading in multiple
regions as of April, 2024. Here, we investigated the virological
properties of KP.2. KP.2 has three substitutions in the S protein
including the two above and an additional substitution in the non-S
protein compared with JN.1 (appendix p 15). We estimated the relative effective reproduction number (Re)
of KP.2 based on the genome surveillance data from the USA, UK, and
Canada, where more than 30 sequences of KP.2 have been reported, using a
Bayesian multinomial logistic model (appendix pp 8–13, 15). The Re of KP.2 is 1·22-times, 1·32-times, and 1·26-times higher than that of JN.1 in the USA, UK, and Canada, respectively (appendix p 15).
These results suggest that KP.2 has higher viral fitness and
potentially becomes the predominant lineage worldwide. Indeed, as of the
beginning of April, 2024, the estimated variant frequency of KP.2 has
already reached 20% in the UK (appendix p 15).
We
then did a neutralisation assay using monovalent XBB.1.5 vaccine sera
and breakthrough infection sera with XBB.1.5, EG.5, HK.3, and JN.1
infections. In all cases, the 50% neutralisation titre against KP.2 was
significantly lower than that against JN.1 (appendix p 15). Altogether, these results suggest that the increased immune escape ability of KP.2 contributes to its higher Re compared with JN.1.
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