How long is spike protein detectable after adenovirus vector vaccines (AstraZeneca ChAdOx1, Johnson & Johnson) vaccination?

1. How these vaccines make spike — the mechanism that matters

Adenoviral‑vector vaccines do not contain spike protein itself but deliver DNA encoding the SARS‑CoV‑2 spike into cells; those cells then transcribe and translate spike which is presented on cell membranes or cleaved into S1/S2 fragments and can be taken up by immune cells — the same basic antigen presentation route described for ChAdOx1 and Ad26 platforms ^{[5] [6] [1]}.

2. Preclinical evidence: spike appears quickly and is measurable for days in animals and in vitro

In cell culture and mouse experiments with ChAdOx1, full‑length spike (S1 and S2) and cleaved S1 were detected in cell pellets and in sera within hours to days after transduction or intramuscular dosing; cryo‑EM and proteomics studies show abundant native‑like spikes on transduced cells in the first 48–72 hours ^{[1] [2] [5]}.

3. Typical expectation from immunology and clinical guidance: weeks, not years, for most people

Clinical guidance and several reviews framed early expectations that vaccine‑generated spike protein and the nucleic acids producing it would be transient — the mRNA/DNA and recombinant spike were expected to be degraded in days to weeks and antigen cleared by immune processes within weeks for most recipients ^{[7] [8] [6]}.

4. Human observational studies show heterogeneity; some detect antigen for months in selected cases

Multiple human reports and reviews document cases where spike antigen or S1 fragments were detected well beyond the initial weeks: studies of post‑infection antigenemia and post‑vaccine syndromes found S1 or spike in monocyte subsets or circulation months after exposure, and one recent decentralized study cited detections from 26 up to 709 days after last known exposure in a subgroup with persistent symptoms ^{[3] [4] [9]}. These findings are largely in selected cohorts (e.g., patients with prolonged symptoms, PASC/PCVS) rather than general population samples ^{[3] [4]}.

5. Differences in assays, sample types and patient selection explain diverging results

Reports vary because researchers measure different targets (full‑length spike vs. S1 fragment), different compartments (blood plasma, monocytes, tissue biopsies), and different populations (healthy volunteers vs. people with persistent symptoms). Proteomics and vaccine‑lot analyses also show vaccine preparations differ in protein content between ChAdOx1 and Ad26, complicating direct comparisons ^{[10] [11] [12]}.

6. Are long detections proof of ongoing spike production from vaccine DNA? Not settled in the literature

Some authors hypothesize persistent antigen may reflect continued expression by cells, trafficking to immune cells, or depot effects; others note possible assay cross‑reactivity, contributions from infection, or detection of fragments/exosomes rather than intact, cell‑surface spike. The sources show hypotheses and observed detections but do not universally demonstrate a single mechanism for long persistence ^{[3] [9] [13]}.

7. Safety signals and context: rare adverse events linked to adenoviral vectors, not necessarily prolonged spike

Adenoviral vaccines were associated with rare syndromes (e.g., vaccine‑induced thrombosis and thrombocytopenia) for which multiple mechanistic explanations have been explored; some literature implicates vector‑related immune effects or PF4 antibodies rather than spike persistence alone ^{[14] [6]}. Preclinical work also ties early spike S1 cleavage to hematologic effects in mice, underscoring biological plausibility for transient antigen effects ^[1].

8. Bottom line and what’s missing from current reporting

Available evidence shows early spike expression after adenoviral vaccination is well established and typically clears within weeks for most people ^{[1] [5] [7]}. Multiple recent and smaller studies report detectable spike or S1 fragments persisting months or longer in selected symptomatic cohorts, but population‑level prevalence, causal mechanisms, and clinical significance remain incompletely described in the cited literature ^{[3] [4] [9]}. Large, controlled longitudinal studies comparing sensitive assays across tissues and matched controls are still needed to resolve how often prolonged detection occurs and what it means clinically — available sources do not provide a definitive population‑level clearance timeline for adenoviral vaccines beyond these mixed findings (not found in current reporting).