PACVS and Long COVID are distinct clinical entities with overlapping biology. Long COVID follows infection, while PACVS follows vaccination without necessarily any prior infection. Both share fatigue, post-exertional malaise, brain fog and dysautonomia, and both are thought to involve spike protein.
PACVS is Post-Acute COVID-19 Vaccination Syndrome. Also known as post-vaccination syndrome (PVS), PCVS and Post-Vac-Syndrom.
At a glance
No, but the two overlap. Long COVID follows infection and PACVS follows vaccination. Both share core symptoms and many candidate mechanisms. Serology (anti-S positive, anti-N negative) helps separate PACVS from infection-related illness.
| Long COVID | PACVS | |
|---|---|---|
| Trigger | SARS-CoV-2 infection | COVID-19 vaccination, without necessarily any prior infection |
| Shared core symptoms | Fatigue, post-exertional malaise, brain fog, dysautonomia | Fatigue, post-exertional malaise, brain fog, dysautonomia |
| Case definition | Defined by the WHO through a modified Delphi consensus process | No agreed diagnostic criteria yet; the PACVS Research Summit is working toward them |
| Spike protein | Thought to be involved | Thought to be involved |
| Endotypes | Patients cluster into endotypes defined by the dominant mechanism | Not yet formally endotyped; the Long COVID framework is a starting hypothesis |
Autoimmune-dominant endotype. GPCR autoantibodies against β-adrenergic, muscarinic and angiotensin AT1 receptors, with prominent dysautonomia and relapsing flares. This is the endotype most consistently described in PACVS cohorts. See the endotypes →
Mechanism by mechanism
The same seven mechanism groups have been proposed for both conditions, but the evidence is further along in Long COVID. In PACVS every group is graded emerging or hypothesis.
| Mechanism | Long COVID | PACVS |
|---|---|---|
| Persistent antigen | Supported Circulating spike and S1 protein within monocytes reported up to 12–15 months after infection.[1,2] | Emerging Higher circulating spike reported in a preprint cohort of people with post-vaccination syndrome; not yet peer-reviewed.[3,4] |
| Immune dysregulation | Supported In 275 people, Long COVID showed altered immune cell populations, higher EBV antibodies and lower cortisol.[5] | Emerging Preprint: fewer memory/effector CD4⁺ T cells, more TNFα⁺ CD8⁺ T cells and more frequent EBV reactivation (42 participants vs 22 controls).[3] |
| Autoimmunity | Emerging Functional GPCR autoantibodies detected in all 31 patients tested.[6] | Emerging In 191 PACVS patients vs 89 vaccinated controls, AT1-receptor and α2B-adrenergic receptor antibodies plus IL-6 separated PACVS from a normal vaccine response.[7] |
| Vascular & clotting | Supported Fibrinolysis-resistant micro-clots, platelet pathology and impaired endothelial function reported in large cohorts.[8,9,10] | Hypothesis Proposed by analogy with Long COVID; no PACVS-specific study has been verified for this page yet. |
| Mitochondria & metabolism | Supported Exercise-induced myopathy, metabolic disturbance and amyloid deposits in muscle worsened after PEM.[11] | Hypothesis Mitochondrial ROS is proposed as a shared mechanism with spike-associated injury in a narrative review; no PACVS muscle studies yet.[12] |
| Autonomic & nerve | Supported POTS and dysautonomia are common, and small-fibre neuropathy was the most frequent finding in a NIH neuropathy evaluation.[13,14] | Emerging Dysautonomia is a defining feature of the PACVS cohort with distinguishing autoantibody markers.[7] |
| Neuroinflammation | Emerging BBB disruption on DCE-MRI in patients with brain fog, with coagulation dysregulation in blood immune cells.[15] | Hypothesis Cognitive symptoms are common, but no PACVS-specific imaging study has been verified for this page. |
Established Replicated and broadly accepted, often as general biology.
Supported Several independent studies in patients with the condition.
Emerging Early or small studies in patients; awaiting replication.
Contested Studies in patients disagree.
Hypothesis Proposed mechanism without direct evidence in this condition.
Telling them apart
Because the symptoms overlap, the distinction rests mainly on history and serology. No single test confirms PACVS.
| Marker | What it shows |
|---|---|
| Anti-spike (anti-S) antibodies | Show prior vaccination or infection. |
| Anti-nucleocapsid (anti-N) antibodies | Specific to infection, because current vaccines don't contain nucleocapsid. Anti-S positive with anti-N negative points away from infection-related illness. |
| Circulating spike or S1 | Measured by ultrasensitive immunoassay or proteomics. |
| Extracellular-vesicle-bound spike | Spike carried on extracellular vesicles may indicate antigen that is still active. |
| Mass spectrometry: vaccine vs viral spike | Spike from mRNA vaccines carries two proline substitutions (K986P, V987P) that viral spike lacks, so mass spectrometry can in principle tell them apart. |
Open question. In people who have had both infection and vaccination, how do you tell vaccine-derived spike from infection-derived spike?
Overlap with ME/CFS
Profound fatigue, post-exertional malaise, unrefreshing sleep and cognitive difficulties. Many people with PACVS meet ME/CFS criteria.
In Long COVID, the metabolic / PEM-dominant endotype is described this way: Severe, reproducible post-exertional malaise with heavy overlap with ME/CFS. Energy metabolism fails under load.
Post-exertional malaise. It often appears 24–72 hours after the activity, which makes triggers hard to identify. Pacing, meaning managing activity to stay within your energy limits, is the main way to manage PEM.
PACVS symptoms → · What is PACVS? → · Biomarker alterations →
References
Grades and notes are taken from the Mechanisms page, where each reference was checked when the page was built.
- Swank Z, Senussi Y, Manickas-Hill Z, et al.. Persistent circulating SARS-CoV-2 spike is associated with post-acute COVID-19 sequelae. Clinical Infectious Diseases 76(3):e487–e490, 2023. doi:10.1093/cid/ciac722
- Patterson BK, Francisco EB, Yogendra R, et al.. Persistence of SARS CoV-2 S1 protein in CD16+ monocytes in post-acute sequelae of COVID-19 (PASC) up to 15 months post-infection. Frontiers in Immunology 12:746021, 2021. doi:10.3389/fimmu.2021.746021
- Bhattacharjee B, Lu P, Monteiro VS, et al.. Immunological and antigenic signatures associated with chronic illnesses after COVID-19 vaccination. medRxiv, 2025. doi:10.1101/2025.02.18.25322379 Preprint
- Halma M, Varon J. Restoring trust in vaccination: listening to patients and acknowledging Post-Acute COVID Vaccine Syndrome. Frontiers in Medicine 12:1688170, 2025. doi:10.3389/fmed.2025.1688170
- Klein J, Wood J, Jaycox JR, et al.. Distinguishing features of long COVID identified through immune profiling. Nature 623:139–148, 2023. doi:10.1038/s41586-023-06651-y
- Wallukat G, Hohberger B, Wenzel K, et al.. Functional autoantibodies against G-protein coupled receptors in patients with persistent Long-COVID-19 symptoms. Journal of Translational Autoimmunity 4:100100, 2021. doi:10.1016/j.jtauto.2021.100100
- Semmler A, Mundorf AK, Kuechler AS, et al.. Chronic fatigue and dysautonomia following COVID-19 vaccination is distinguished from normal vaccination response by altered blood markers. Vaccines 11(11):1642, 2023. doi:10.3390/vaccines11111642
- Pretorius E, Vlok M, Venter C, et al.. Persistent clotting protein pathology in Long COVID/PASC is accompanied by increased levels of antiplasmin. Cardiovascular Diabetology 20:172, 2021. doi:10.1186/s12933-021-01359-7
- Pretorius E, Venter C, Laubscher GJ, et al.. Prevalence of symptoms, comorbidities, fibrin amyloid microclots and platelet pathology in individuals with Long COVID/PASC. Cardiovascular Diabetology 21:148, 2022. doi:10.1186/s12933-022-01579-5
- Charfeddine S, Ibn Hadj Amor H, Jdidi J, et al.. Long COVID 19 syndrome: is it related to microcirculation and endothelial dysfunction? Insights from TUN-EndCOV study. Frontiers in Cardiovascular Medicine 8:745758, 2021. doi:10.3389/fcvm.2021.745758
- Appelman B, Charlton BT, Goulding RP, et al.. Muscle abnormalities worsen after post-exertional malaise in long COVID. Nature Communications 15:17, 2024. doi:10.1038/s41467-023-44432-3
- Lee E, Ozigbo AA, Varon J, Halma M, et al.. Mitochondrial reactive oxygen species: a unifying mechanism in long COVID and spike protein-associated injury: a narrative review. Biomolecules 15(9):1339, 2025. doi:10.3390/biom15091339
- Davis HE, McCorkell L, Vogel JM, Topol EJ. Long COVID: major findings, mechanisms and recommendations. Nature Reviews Microbiology 21:133–146, 2023. doi:10.1038/s41579-022-00846-2
- Oaklander AL, Mills AJ, Kelley M, et al.. Peripheral neuropathy evaluations of patients with prolonged long COVID. Neurology: Neuroimmunology & Neuroinflammation 9(3):e1146, 2022. doi:10.1212/nxi.0000000000001146
- Greene C, Connolly R, Brennan D, et al.. Blood–brain barrier disruption and sustained systemic inflammation in individuals with long COVID-associated cognitive impairment. Nature Neuroscience 27:421–432, 2024. doi:10.1038/s41593-024-01576-9
This page is educational and does not provide medical advice.