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How long is spike protein detectable after Moderna (mRNA-1273) vaccination?
Executive Summary
Moderna’s mRNA-1273 vaccine leads to detectable spike protein in some people for periods ranging from hours/days to many months, with most controlled clinical studies showing clearance within days to weeks but several postmortem and observational reports documenting persistence in tissues or plasma for months to over a year in selected cases. The evidence divides into short-term controlled detections tied to immune response, and a smaller set of pathology-focused or syndrome-linked studies that report longer, sometimes very prolonged detection; each body of work uses different methods, sample types, and patient groups, so direct comparisons require caution [1] [2] [3] [4].
1. What proponents claim: multiple studies report spike protein beyond the acute window
Several published and preprint analyses report spike protein or vaccine mRNA detectable beyond the initial days after vaccination, sometimes in unexpected tissues. Early clinical work showed circulating vaccine antigen detectable as soon as day one after mRNA-1273 injection and correlated clearance with rising IgG/IgA, indicating the immune system typically eliminates detectable antigen over days to weeks [1]. Pathology-oriented studies have detected vaccine mRNA or spike protein in axillary lymph nodes within 30 days after vaccination and in cardiac tissue associated with healing myocardial injury, suggesting local persistence linked to tissue damage or inflammation [2]. These findings are often framed as observations that warrant mechanistic follow-up rather than definitive evidence of widespread long-term persistence [2] [1].
2. Short-term controlled studies: a clear pattern of rapid clearance in most people
Controlled cohort studies show a pattern of rapid appearance and clearance of spike antigen in plasma, with most vaccine recipients losing measurable circulating antigen as antibodies rise. Clinical Infectious Diseases and related reports documented antigen detectable early after dosing but associated antigen disappearance with mounting IgG/IgA responses; these studies do not support sustained, generalized circulation of spike protein in healthy vaccinees beyond a few days to a few weeks [1]. Circulation of unbound full-length spike was, however, reported in a small group of adolescents and young adults with postvaccine myocarditis up to about three weeks post-vaccination, contrasting with matched asymptomatic controls who had no detectable free spike [5] [6]. These data underline that short-term detection is common but long-term systemic circulation in asymptomatic people is not the dominant finding.
3. Medium- and long-term signals: tissue studies and syndrome-linked reports claim persistence
A smaller body of work—postmortem tissue analyses and observational studies of people with prolonged symptoms—reports spike protein or mRNA persisting for months, up to at least 17 months in some tissue samples, and over 700 days in a minority of patients with post-vaccination syndromes. Postmortem axillary node studies found vaccine mRNA within 30 days but not in many visceral organs; separate cerebral artery analyses detected spike protein up to 17 months after mRNA vaccination in a subset of hemorrhagic stroke cases, and a 2025 Yale cohort reported detectable spike protein in some individuals more than 700 days after vaccination [2] [4] [3]. These studies use different assays and sample types—tissue immunohistochemistry or PCR vs. plasma antigen assays—and focus on specific patient groups, often with underlying pathology, which limits generalization to the broader vaccinated population.
4. Competing interpretations: causation, sampling, assay limits, and selection bias
Conflicting interpretations arise from methodological differences: assay sensitivity/specificity, whether measurement detects intact, functional spike versus fragments, and selection of patients with tissue injury or prolonged symptoms influence findings. Some tissue detections correlate with healing injury, suggesting local uptake at damage sites rather than vaccine-driven pathology; others observe unbound full-length spike in myocarditis patients but not in asymptomatic controls, implying a possible mechanistic link in rare adverse events [2] [5]. Small sample sizes, convenience sampling (postmortem cases, stroke or myocarditis patients), and absence of longitudinal population-level surveillance mean that reports of long persistence should not be interpreted as proof of widespread, long-term circulating spike after vaccination [2] [4] [5].
5. Bottom line, uncertainty, and research priorities for public health decisions
The evidence establishes that spike protein is transiently detectable in most vaccine recipients early after mRNA-1273 vaccination and that rare, selectively sampled cases show prolonged tissue or plasma detection. There is no consensus that long-term persistence is common, nor definitive proof that detected long-term protein causes adverse outcomes; however, the findings identify clear priorities: standardized assays cross-validating plasma versus tissue detection, larger longitudinal cohorts including asymptomatic controls, and mechanistic studies linking persistence to clinical effects. Policy and clinical evaluation should balance the large body of safety data showing benefit with targeted investigation into the minority of cases where prolonged detection is reported [1] [3] [4].