The persistent post-vaccination symptoms, commonly referred to as post-COVID-19 vaccination syndrome (PCVS), include new-onset cardiac, vascular, and neurological symptoms that can manifest within minutes to hours of vaccination and, in many cases, last for months or even years. The symptomatology of PCVS closely mirrors that of post-acute sequelae of COVID-19 (PASC, or Long COVID), suggesting that their pathophysiological mechanisms may be similar. In their earlier studies, the American research team demonstrated that the S1 subunit of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein persisted in non-classical and intermediate monocytes for months to years after an acute infection, which may have contributed to PASC. Since approved COVID-19 vaccines (Pfizer, Moderna, Janssen, AstraZeneca) deliver synthetic S1 to elicit immunity, this study, conducted by the same research team, investigated whether the persistence of vaccine-derived S1 protein in CD16+ monocytes can maintain inflammation and contribute to post-COVID-19 vaccination syndrome.
About the study
The study included participants who had received at least one dose of an approved SARS-CoV-2 vaccine, BNT162b2 (Pfizer), mRNA-1273 (Moderna), Janssen (Johnson & Johnson), or ChAdOx1 nCoV-19 (AstraZeneca), and reported new-onset symptoms lasting more than 30 days after COVID-19 vaccination, as well as asymptomatic vaccinated controls.
Exclusion criteria were a prior history of seizures, migraines, neuropathy, inflammatory bowel disease, depression, anxiety disorders, chronic fatigue syndrome, Lyme disease, fibromyalgia, arthritis, chronic obstructive pulmonary disease, asthma, diabetes, chronic kidney disease, chronic heart failure, arrhythmias, bleeding disorders, or if the participants were on anticoagulation therapy. Those with a documented history of positive polymerase chain reaction (PCR) tests for SARS-CoV-2, positive tests for anti-SARS-CoV-2 nucleocapsid antibodies (indicating past natural infection), or positive T-Detect tests (indicating SARS-CoV-2-specific T-cell responses) were also excluded. These criteria were assessed through patient clinical history and laboratory testing conducted before enrollment.
Blood specimens were taken between 38 and 245 days from the last COVID-19 vaccination (mean: 105 days for the study group and 97 days for the control group). Three analytical approaches were employed: machine learning-based immune profiling to compare cytokine signatures of PCVS with those of PASC, flow cytometry to detect the persistence of the S1 in CD16+ monocyte subsets, and liquid chromatography-mass spectrometry to confirm the presence of the S1 subunit of the SARS-CoV-2 spike protein and related peptides across different vaccine types. The possible correlations between the persistence of S1, symptoms of post-COVID-19 vaccination syndrome, and inflammatory markers were also explored.
Results
50 symptomatic individuals (mean age 42 years, ranging from 13 to 65 years, 36 females and 14 males) and 26 asymptomatic vaccinated controls (mean age 40 years, ranging from 20 to 70 years, 16 females and 10 males) were included in this study. Previous SARS-CoV-2 infection was excluded by clinical history, anti-nucleocapsid antibody tests, and T-Detect assays. In the symptomatic group, 32/50 patients received one dose of vaccine and 18/50 patients received two doses. Most of them were vaccinated with BNT162b2, Pfizer (27 patients), followed by mRNA-1273, Moderna (15 patients), Janssen, Johnson & Johnson (7 patients), or ChAdOx1 nCoV-19, AstraZeneca (1 patient). The predominant post-vaccination symptoms were fatigue (27/50), neuropathy (27/50), brain fog (22/50), and headache (23/50), and varied according to vaccine type. In the group of control individuals, 23/26 people received two doses of either BNT162b2, Pfizer, or mRNA-1273, Moderna, and the remaining three controls received one dose of the Janssen vaccine.
Given the symptomatic overlap with PASC and the absence of an ongoing replication-competent virus, researchers applied machine learning to a 14-plex cytokine panel from 50 symptomatic individuals. The results showed that the symptomatic group had significantly increased levels of interleukin (IL)-4, C-C motif chemokine ligand (CCL)3, CCL5 (RANTES), soluble CD40 Ligand (sCD40L), vascular endothelial growth factor (VEGF) and IL-8, and downregulated tumor necrosis factor (TNF)-alpha and granulocyte-macrophage-colony-stimulating factor (GM-CSF) compared to controls. Most inflammatory cells can express CCL5, among them, T cells and monocytes are the most common types of CCL5-expressing cells. CCL5 has the highest affinity to CCR5, a G-protein-coupled receptor expressed on T cells, smooth muscle endothelial cells, epithelial cells, and even parenchymal cells, etc. On the other hand, GM-CSF plays a role in promoting monocyte maturation into macrophages and dendritic cells, thus, GM-CSF decrease, as observed in this study, could limit this process, potentially favoring the persistence of less differentiated monocytes, such as non-classical monocytes. According to the authors, these profiles aligned with PASC-like features, except for IL-8.
A comparison of cytokine levels between individuals assessed before 120 days from the last vaccination and those at 120 days or beyond the last vaccination showed that none of the biomarkers differed between the two groups. These findings indicate relatively stable cytokine levels between the two-time points.
A correlation analysis tied these cytokines to specific symptoms. IL-2, CCL3, and VEGF correlated positively with shortness of breath, and sCD40L with twitching, tremors, fatigue, and brain fog. Interestingly, fatigue was negatively correlated with IL-10, GM-CSF, TNF-alpha, and VEGF.
To explore the cellular basis, researchers examined the presence of S1 protein in monocyte subsets from 12 symptomatic patients and 10 controls using flow cytometry. Up to 245 days after vaccination, 92% (11/12) of symptomatic patients had significantly elevated S1 levels in non-classical monocytes, and 67% (8/12) in intermediate monocytes. The S1 was also detected in intermediate monocytes of one control subject (1/10). Liquid chromatography-mass spectrometry confirmed S1, S2, and mutant S1 peptides in CD16+ cells across all vaccine types- unlike PASC, where only S1 was detected.
A correlation analysis demonstrated that S1 persistence in intermediate monocytes correlated with sensory hypersensitivity, tinnitus, tachycardia, postural orthostatic tachycardia syndrome (POTS), and headaches. The S1 persistence in non-classical monocytes correlated with vision disturbances, POTS, fatigue, and headaches, and in classical monocytes with menstrual irregularities, sensory hypersensitivity, tachycardia, joint pain, and headaches.
Conclusion
These findings suggest that the persistence of vaccine-derived S1 protein in CD16+ monocytes, and PASC-like cytokine profile, may contribute to persistent post-COVID-19 vaccination syndrome. The authors stated that although S1 was detected, causality remains unproven due to limited sample size and variable S1 presence. However, the unique presence of S2 and mutant S1 peptides raises questions about vaccine-specific effects, though their clinical roles remain unclear. Additionally, the detection of S1 in one control subject suggests that it may not be exclusive to symptomatic post-COVID-19 vaccination syndrome.
The authors concluded that larger, longitudinal studies with advanced infection screening are needed to confirm these associations, explore the impacts of S2/mutant S1, and test interventions targeting CCR5 or VEGF signaling pathways.
This article was published in Human Vaccines & Immunotherapeutics.
Journal Reference
Patterson BK, Yogendra R, Francisco EB, et al. Detection of S1 spike protein in CD16+ monocytes up to 245 days in SARS-CoV-2-negative post-COVID-19 vaccine syndrome (PCVS) individuals, Human Vaccines & Immunotherapeutics, 2025; 21:1, 2494934 (Open Access). https://doi.org/10.1080/21645515.2025.2494934
