NPPA and infection: To address this question, we first tested serum neutralization against vesicular stomatitis virus (VSV) pseudotyped KP.3.1.1, XEC, and XEC individual spike mutations on KP.3 (KP.3-T22N and KP.3-F59S) compared to JN.1, KP.2, and KP.3, using samples from two cohorts of adults: (1) participants with a history of JN.1 sublineage infection during 2024, sampled 32–87 days after infection (“JN.1 infx”), and (2) participants who received an updated KP.2-based mRNA monovalent vaccine booster, sampled approximately 4 weeks after dosing (“KP.2 MV”) (Tables S2 and S3).