Growing evidence from laboratory studies and large patient databases suggests that COVID-19 may raise the risk of developing Parkinson’s disease, though the link is far from settled. Several biological mechanisms have been identified in animal and cell models, and population-level data show a temporary uptick in new Parkinson’s diagnoses in the months following SARS-CoV-2 infection. Whether COVID-19 will ultimately prove to be a meaningful driver of Parkinson’s on a population scale, or a modest contributor in people who were already vulnerable, is one of the more closely watched questions in neurology right now.
What Population Data Actually Show
The strongest signal so far comes from retrospective studies that tracked people after a COVID-19 diagnosis and compared their rates of new Parkinson’s disease against matched controls. A two-year retrospective cohort study found significantly increased odds of new-onset Parkinson’s disease in the COVID-19 group at three, six, nine, and twelve months after infection, with the peak at six months. After twelve months, the difference between the two groups was no longer statistically significant.1PubMed. Frequency of Parkinson disease following COVID-19 infection: A two-year retrospective cohort study A separate systematic review and meta-analysis noted that in one large cohort of over 236,000 COVID-19 patients, about 0.11% were diagnosed with parkinsonism within six months of follow-up.2Annals of Medicine and Surgery. New-onset Parkinsonism as a Covid-19 infection sequela: A systematic review and meta-analysis
These numbers sound small in absolute terms, but Parkinson’s typically develops over years. Seeing even a modest spike within months of an infection is unusual enough to prompt concern. The fact that the elevated risk in the cohort study faded after twelve months complicates interpretation: it could mean the virus triggers a temporary parkinsonism that resolves, or it could mean the early signal reflected diagnostic attention bias during the acute pandemic period. Longer-term follow-up, which is now becoming available, will be critical to sorting this out.
How SARS-CoV-2 Reaches the Brain
For the virus to contribute to a brain disease, it needs a way in. Autopsy and imaging studies have provided evidence that SARS-CoV-2 can invade the central nervous system through the olfactory nerve, the bundle of neurons that carries smell signals from the nose to the brain. Researchers examining tissue from deceased COVID-19 patients found viral RNA along this pathway, suggesting the virus travels from the nasal lining through the olfactory tract and into deeper brain structures.3Nature Neuroscience. Olfactory transmucosal SARS-CoV-2 invasion as a port of central nervous system entry in individuals with COVID-19 Viral RNA was also detected in brain regions with no direct olfactory connection, such as the cerebellum, which points to additional routes of entry. These could include infected immune cells crossing from the bloodstream into the brain, or the virus breaching the blood-brain barrier directly.4PubMed Central. Can SARS-CoV-2 infect the central nervous system via the olfactory bulb or the blood-brain barrier?
This matters for the Parkinson’s connection because the olfactory pathway leads into brain regions adjacent to areas rich in dopamine-producing neurons, the very cells that die off in Parkinson’s disease. If the virus gains a foothold in those neighborhoods, it’s positioned to cause trouble in the cells that matter most.
Why Dopamine Neurons May Be Especially Vulnerable
SARS-CoV-2 latches onto cells using a receptor called ACE2 as its entry point. Lab work using human stem-cell-derived dopamine neurons confirmed that these neurons do express ACE2 on their surface, making them susceptible to infection.5Cell Stem Cell. SARS-CoV-2 infection of human pluripotent stem cell-derived dopaminergic neurons implicates a causative role in Parkinson’s disease pathogenesis This is a meaningful detail because the progressive death of dopamine-producing neurons in a brain region called the substantia nigra is the hallmark of Parkinson’s disease. If SARS-CoV-2 can enter and damage these cells directly, it could accelerate or initiate the degenerative process that defines the disease.
The Alpha-Synuclein Problem
Parkinson’s disease is characterized by the buildup of misfolded clumps of a protein called alpha-synuclein inside neurons. These toxic clumps spread from cell to cell and eventually kill the neurons they accumulate in. Multiple lab studies now show that a piece of the SARS-CoV-2 virus, specifically the S1 portion of its spike protein, can accelerate the clumping of alpha-synuclein. In rodent models, the S1 protein triggered alpha-synuclein aggregation alongside activation of the brain’s resident immune cells.6PubMed Central. SARS-CoV-2 Spike Protein 1 Causes Aggregation of α-Synuclein via Microglia-Induced Inflammation and Production of Mitochondrial ROS In cell culture, the S1 protein was found to interact directly with alpha-synuclein, promoting its aggregation and causing mitochondrial dysfunction and oxidative stress. Alarmingly, the alpha-synuclein fibrils seeded by S1 showed enhanced ability to propagate further clumping in neighboring cells.7PubMed. SARS-CoV-2 Spike Protein S1 Domain Accelerates α-Synuclein Phosphorylation and Aggregation in Cellular Models of Synucleinopathy
A recent study went further by injecting the S1 protein intravenously into animals, finding that it caused neuroinflammation and alpha-synuclein accumulation specifically in brain regions relevant to Parkinson’s disease.8PubMed. Intravenous SARS-CoV-2 Spike protein induces neuroinflammation and alpha-Synuclein accumulation in brain regions relevant to Parkinson’s disease This is significant because it suggests the spike protein doesn’t even need to reach the brain through direct viral infection of neurons; circulating fragments from a systemic infection could be enough to kick off Parkinson’s-related pathology in vulnerable brain areas.
A caveat here: these are laboratory and animal findings. They demonstrate a plausible mechanism, not proof that this happens at meaningful levels inside living humans during a typical COVID-19 infection. The doses used in experiments often exceed what the brain would actually encounter. Still, the consistency of the findings across different research groups and experimental designs is what gives neuroscientists reason to take the connection seriously.
Neuroinflammation as the Amplifier
If the spike protein and alpha-synuclein interaction is the spark, neuroinflammation is the accelerant. The brain’s immune cells, called microglia, switch into an aggressive inflammatory mode when they encounter pathogens or abnormally folded proteins. In COVID-19, the virus and its spike protein both activate microglia, which then produce a flood of inflammatory molecules and reactive oxygen species that damage surrounding neurons.9PubMed Central. Neuroinflammation and Oxidative Stress in Parkinson’s Disease, Alzheimer’s Disease, and COVID-19 This creates a destructive feedback loop: inflammation drives more alpha-synuclein misfolding, which activates more microglia, which generates more inflammation.
Separate experiments on human microglia exposed to the SARS-CoV-2 spike protein showed increased production of inflammatory cytokines and reactive oxygen species, along with disrupted mitochondrial function and increased cell death.10PubMed Central. Mitochondrial Dynamics in SARS-COV2 Spike Protein Treated Human Microglia: Implications for Neuro-COVID Mitochondrial dysfunction is itself a well-established feature of Parkinson’s disease, so SARS-CoV-2 may be compounding a vulnerability that already exists in the dopamine neurons of people predisposed to the condition.
Loss of Smell as a Shared Warning Sign
One of the earliest and most common symptoms of COVID-19 was loss of smell. This same symptom is also one of the earliest warning signs of Parkinson’s disease, often appearing years before motor symptoms like tremor or stiffness. The overlap is not a coincidence of trivia but a reflection of shared anatomy: both conditions affect the olfactory bulb and the brain regions it connects to.11PubMed Central. Long COVID: From olfactory dysfunctions to viral Parkinsonism
Researchers have proposed that both COVID-19 and Parkinson’s disease may impair smell through damage to the regenerative capacity of neurons in the olfactory bulb. Normally, the olfactory system is one of the few brain regions where new neurons are continuously generated throughout life. When that renewal process is disrupted, whether by viral infection or by the degenerative process of Parkinson’s, the result is the same: persistent loss of smell.12Journal of Chemical Neuroanatomy. COVID-19 and Parkinson’s disease: Defects in neurogenesis as the potential cause of olfactory system impairments and anosmia This raises the question of whether people who developed persistent loss of smell after COVID-19 should be monitored more closely for early signs of neurodegeneration in the years ahead.
Blood biomarker data add a layer to this concern. Post-COVID patients with lingering smell problems showed moderately elevated levels of neurofilament light chain, a protein that leaks into the blood when nerve fibers are damaged, compared to healthy controls.13PubMed Central. Insight into NeuroCOVID: neurofilament light chain (NfL) as a biomarker in post-COVID-19 patients with olfactory dysfunctions Elevated neurofilament light chain is not specific to Parkinson’s; it rises in many neurological conditions. But its presence in people with post-COVID smell loss suggests ongoing nerve damage that goes beyond a simple stuffed nose.
The Autoimmune Angle
Another route by which COVID-19 could harm the brain has nothing to do with the virus directly entering neurons. SARS-CoV-2 is notorious for triggering autoimmune responses, where the body’s immune system mistakenly attacks its own tissues. Studies of COVID-19 patients with neurological complications have found an unexpectedly high rate of autoantibodies targeting brain tissue. In one multicenter study, autoantibodies were confirmed in a large proportion of tested samples from patients with COVID-associated central nervous system syndromes, including cases of encephalitis, encephalopathies, and, in at least one patient, Parkinson’s disease.14PubMed. High Frequency of Autoantibodies in COVID-19 Patients with Central Nervous System Complications: a Multicenter Observational Study
A separate study found that all tested COVID-19 patients with neurological symptoms showed anti-neuronal autoantibodies in their blood or spinal fluid. Some of these antibodies targeted proteins in brain structures relevant to Parkinson’s disease, including the basal ganglia and the olfactory bulb.15Brain, Behavior, and Immunity. High frequency of cerebrospinal fluid autoantibodies in COVID-19 patients with neurological symptoms The worry is that even after the virus is cleared, these self-targeting antibodies could continue causing damage to dopamine neurons, essentially setting a slow-burning autoimmune process in motion.
The Genetics Question
If COVID-19 truly causes Parkinson’s disease, you might expect to find shared genetic underpinnings that make people susceptible to both conditions. Researchers tested this using a method that examines genetic variants across large populations to look for causal relationships. The result was essentially null: no genetic causal link was found between susceptibility to SARS-CoV-2 infection, COVID-19 severity, or hospitalization rates and the risk of Parkinson’s disease. The reverse direction also showed nothing: having the genetic variants associated with Parkinson’s did not increase susceptibility to COVID-19.16Frontiers in Neurology. No genetic link between Parkinson’s disease and SARS-CoV-2 infection: a two-sample Mendelian randomization study
This doesn’t disprove the COVID-Parkinson’s connection, but it does narrow how we should think about it. The link, if it exists, is probably not about shared genetic vulnerability. Instead, it appears to be about what the virus does once it’s in the body: the inflammation, the protein misfolding, and the immune disruption described above. In other words, the risk would come from the infection itself, not from an underlying genetic predisposition to both conditions.
The Gut-Brain Connection
One increasingly studied theory of Parkinson’s disease holds that the disease may begin in the gut before spreading to the brain via the vagus nerve. COVID-19 is relevant here because SARS-CoV-2 frequently infects the gastrointestinal tract, causing inflammation and disrupting the gut microbiome. Researchers have highlighted that virus-induced gut inflammation, microbial imbalance, and elevated alpha-synuclein in the intestines could feed into this gut-to-brain pathway, potentially adding another mechanism by which COVID-19 might contribute to Parkinson’s risk.17PubMed Central. Viral Infection-Induced Gut Dysbiosis, Neuroinflammation, and α-Synuclein Aggregation: Updates and Perspectives on COVID-19 and Neurodegenerative Disorders This remains speculative in the specific context of COVID-19, but it aligns with what we know about both the virus’s gastrointestinal effects and the broader Parkinson’s research landscape.
What About People Who Already Have Parkinson’s
For people living with Parkinson’s disease before the pandemic, COVID-19 brought a double burden. A community-based case-control study found that Parkinson’s patients who contracted COVID-19 experienced significant worsening of both motor and nonmotor symptoms. About a third of cases required adjustments to their medication. The clinical deterioration resulted from both the infection itself and impaired absorption and metabolism of dopaminergic drugs during the illness. Fatigue and urinary problems were the most prominent nonmotor issues.18PubMed Central. Effects of COVID-19 on Parkinson’s Disease Clinical Features: A Community-Based Case-Control Study
Beyond the direct effects of infection, pandemic-era lockdowns and healthcare disruptions took their own toll. Parkinson’s patients showed worsened motor symptoms and faster disease progression during periods of pandemic-related restrictions compared to before the outbreak.19PubMed. Worsened Parkinson’s Disease Progression: Impact of the COVID-19 Pandemic Reduced physical activity, disrupted therapy schedules, social isolation, and difficulty accessing rehabilitation services all contributed. For Parkinson’s patients, exercise and consistent medication timing are therapeutic cornerstones, and the pandemic undermined both.
Lessons From Past Pandemics
The idea that a viral pandemic could trigger a wave of parkinsonism is not new. After the 1918 Spanish flu pandemic, a mysterious condition called encephalitis lethargica swept through populations worldwide, leaving many survivors with severe Parkinson’s-like symptoms. For decades, the assumption was that the influenza virus caused the neurological damage. But modern analysis of archival brain samples largely failed to confirm a direct relationship between influenza and encephalitis lethargica.20PubMed Central. The relationship between encephalitis lethargica and influenza: a critical analysis Epidemiological analyses suggest the two outbreaks may have been coincidental rather than causally linked.
A broader review of influenza-associated parkinsonism throughout the twentieth and twenty-first centuries found that remarkably little parkinsonism was reported in connection with influenza, with the notable exception of the cases originally described in the encephalitis lethargica era.21PubMed Central. Parkinsonism and neurological manifestations of influenza throughout the 20th and 21st centuries This history is a useful reminder that the link between any given virus and parkinsonism can take decades to clarify and may turn out to be weaker than initial alarm suggested. Various viruses have been described as having the potential to induce or contribute to parkinsonism, but the relationship between viral infection and Parkinson’s disease remains debated.22PubMed Central. Viruses, parkinsonism and Parkinson’s disease: the past, present and future
Drug Repurposing and Therapeutic Overlaps
One practical outcome of studying the COVID-Parkinson’s intersection has been a closer look at medications that might work against both conditions. Amantadine, a drug that has been used for decades to treat Parkinson’s symptoms, also has antiviral properties. It was explored as a potential COVID-19 treatment because it can interfere with the process viruses use to enter cells and replicate. A review flagged amantadine specifically as a drug approved across developed countries that possesses both antiviral activity against SARS-CoV-2 and anti-Parkinson’s effects.23PubMed. Targeting COVID-19 in Parkinson’s Patients: Drugs Repurposed Whether this dual action translated into meaningful protection for Parkinson’s patients who contracted COVID-19 is still unclear, but the overlap highlights how interconnected these pathways can be.
More broadly, the recognition that vaccination reduces viral infections has prompted researchers to ask whether vaccines could have neuroprotective effects beyond their primary purpose. Some data have associated vaccinations with reduced risk of dementia, raising the question of whether preventing infections like COVID-19 could lower the odds of neurodegenerative disease downstream.24PubMed Central. Could targeting viruses be a new hope against neurodegenerative diseases? This idea remains early-stage and should not be overstated, but it represents a shift in how scientists are thinking about the relationship between infections and brain health over a lifetime.