What studies have measured circulating spike protein levels after mRNA COVID-19 vaccination?
Executive summary
Several research teams have measured circulating SARS‑CoV‑2 spike protein following mRNA COVID‑19 vaccination: a peer‑reviewed plasma study linked free full‑length spike to post‑vaccine myocarditis (mean ~33.9 pg/mL) [1], and a Yale‑led study reported detectable spike in some people with a proposed “post‑vaccination syndrome” — including traces more than 700 days after last dose in a subset of participants [2]. Reviews and commentaries note exosomes or soluble spike detectable up to months after vaccination and call for more study of persistence and clinical significance [3].
1. What the published measurements show: quantified spike in select cohorts
A controlled plasma study of adolescents and young adults who developed myocarditis after mRNA vaccination reported markedly higher levels of free, full‑length spike protein in affected patients (33.9 ± 22.4 pg/mL) while asymptomatic vaccinated controls had no detectable free spike, a statistically significant difference [1]. That paper gives the clearest numeric evidence that circulating full‑length spike can be measured after vaccination in specific clinical settings [1].
2. Wider study reporting: Yale’s findings on long persistence in a subset
Yale’s LISTEN cohort work, described in Yale News and widely reported, found that “typically spike protein can be detected for a few days after vaccination,” but some participants with symptoms ascribed to a post‑vaccination syndrome (PVS) had detectable spike more than 700 days after their last vaccine dose; the team linked spike persistence as one of several biological differences in the symptomatic group [2]. The Yale report is a small, cohort‑based observation and the authors say they are investigating mechanisms including autoimmunity and viral reactivation [2].
3. Reviews and mechanistic discussion: soluble/exosomal spike and unresolved questions
A 2025 immunology review frames the question at the mechanistic level: soluble spike or spike carried on exosomes has been detected in plasma of vaccinated subjects up to about four months in cited literature, raising the question whether these circulating forms drive protective immunity or excessive inflammation; the review calls for further research into tissue localization and host factors that could prolong spike production [3]. That review does not give a single definitive timeline but highlights mechanisms and uncertainty [3].
4. Clinical context: when detectable spike has been associated with symptoms
Journalistic coverage and the Yale report tie detectable spike to two contexts in the current reporting: a rare post‑vaccination myocarditis cohort with higher free full‑length spike [1] and a small group reporting PVS with persistent spike in some participants [2] [4]. These are observational findings in select cohorts; causation, prevalence in the general vaccinated population, and clinical consequences remain debated in the sources [2] [1] [4].
5. Conflicting narratives and media amplification
Media and online outlets have amplified these findings differently. Fact‑checking and mainstream outlets have cautioned that detectable spike in specific subgroups is not equivalent to proof of widespread, long‑term spike production or DNA integration; Snopes summarized early claims around a Yale paper and emphasized that frequency and clinical significance were unclear pending peer review [5]. Conversely, some advocacy or non‑peer sources have framed prolonged spike as definitive evidence of harm; that framing is not supported by the peer‑reviewed myocarditis paper or Yale’s reporting, which both call for additional research [6] [2] [1].
6. What is not established in the available reporting
Available sources do not provide a population‑level estimate of how often circulating spike persists long term in otherwise healthy vaccinated people, nor do they show a proven causal pathway from vaccine mRNA to permanent DNA alteration — the Yale reporting and Snopes note hypotheses and speculation but stop short of definitive claims [2] [5]. Broad safety conclusions and frequency estimates are not contained in the cited materials [5] [2] [1].
7. Bottom line for readers and researchers
Multiple peer‑reviewed and institutional reports document measurable circulating spike in certain post‑vaccine clinical scenarios (notably post‑vaccine myocarditis at ~33.9 pg/mL) and small cohorts with persistent detection up to ~700 days; reviews urge mechanistic follow‑up to determine cause and clinical relevance [1] [2] [3]. Competing narratives exist: some outlets emphasize uncertainty and need for replication [5] [2], while other non‑academic sources amplify claims of long‑term harm without the supporting population‑level data provided in the peer‑reviewed literature [6]. Available reporting points to a clear research priority: larger, prospective studies that quantify circulating spike over time across representative vaccinated populations and tie those measures to clinical outcomes [3] [2] [1].