Post-COVID SARS-CoV-2 Antigen Persistence: A Critical Review of Mass Spectrometry Methodology and the Confound of Vaccine-Derived Antigens

ABSTRACT: Persistent SARS-CoV-2 antigen has been proposed as a driver of post-COVID condition (PCC), with targeted mass spectrometry multiple reaction monitorin/selected reaction monitoring (MRM/SRM) increasingly invoked as quantitative evidence. We appraise the targeted-MS literature on SARS-CoV-2 antigen in genuine human clinical specimens and re-analyse a focal study, which reported spike and nucleocapsid “protein” concentrations in ng/µL from two proteotypic peptides per target with ¹³C/¹⁵N internal standards. These values are either physically impossible as intact protein or, more likely, raw peptide concentrations reported without the required ≈122-fold molecular-weight correction. Only 15 of 65 patients (26%) had cellular pellet spike above the authors’ own limit of quantification; nucleocapsid was essentially undetectable; and in those 15, the nucleocapsid: spike molar ratio was strongly inverted relative to intact virions, incompatible with a viral source. Critically, no targeted-MS method has ever quantified spike in human blood—the prior literature is nucleocapsid detection in respiratory specimens and spike quantification in vaccine or recombinant material—so the reported blood-spike values lack any validated precedent and exceed the most sensitive validated platform (single-molecule arrays) by several orders of magnitude, with no enrichment step. Finally, 77% of the cohort was vaccinated, and a measurable spike was concentrated among vaccinated individuals. The source’s own supplement inconsistently reports vaccination status. Their 2024 predecessor publication withheld it entirely. The MRM/SRM data, therefore, do not support persistent viral antigen as a general driver of PCC. Minimum standards are proposed: molar reporting, strict limit-of-quantification (LOQ) compliance, qualifier-ion confirmation, vaccine-discrimination peptides, stoichiometric cross-validation, and vaccination-status disclosure. We suggest that the cellular blood component, routinely discarded, warrants direct investigation in the context of spike persistence and PCC symptoms.