COVID-19 affects far more than just the lungs. The virus can damage the heart, brain, kidneys, gut, and blood vessels, causing effects that range from a mild cold to life-threatening organ failure. Some people recover in days, while others develop symptoms that persist for months or years. Here’s what the virus does to the body during acute infection and beyond.
How the Virus Enters Your Cells
SARS-CoV-2 gets inside your cells by latching its spike protein onto a receptor called ACE2, which sits on the surface of cells throughout your body. ACE2 is present in the lungs, heart, kidneys, blood vessels, gut lining, pancreas, brain, and even the tongue. That wide distribution explains why COVID-19 can affect so many different organ systems at once.
In the lungs, ACE2 is most abundant on cells that maintain the tiny air sacs where oxygen enters your blood. When the virus hijacks these cells, it reduces the number of working ACE2 receptors on the surface, which disrupts the normal protective functions those receptors serve. The virus also targets blood vessel walls directly, since vascular cells are major ACE2 carriers. This vascular involvement is a key reason COVID-19 triggers clotting problems and inflammation far from the respiratory tract.
Common Symptoms During Acute Infection
A large meta-analysis across multiple studies found fever in about 81% of confirmed cases, cough in 59%, and fatigue in 39%. Shortness of breath appeared in roughly 26% of patients. These numbers reflect the earlier, more severe waves of infection; milder variants and widespread immunity have shifted the typical presentation closer to an upper respiratory illness for many people, though severe disease still occurs.
Digestive symptoms are more common than many people realize. About 7% of patients report diarrhea and nearly 5% experience nausea or vomiting. Viral genetic material has been detected in stool samples in over 40% of patients, suggesting the virus actively replicates in the gut even when digestive symptoms are mild or absent.
What Happens in the Lungs
The hallmark of COVID-19 pneumonia is a pattern called ground-glass opacities on chest imaging, hazy patches that indicate inflammation and fluid in lung tissue. In early disease, these appear as scattered spots, often near the outer edges of the lungs. As the illness progresses, these patches can merge and spread, eventually replacing healthy, air-filled tissue with dense, non-functioning tissue.
In severe cases, the lung damage meets the criteria for acute respiratory distress syndrome (ARDS), a condition where the lungs become so inflamed and fluid-filled that they can no longer deliver enough oxygen to the blood. Patients with severe COVID pneumonia typically show oxygen saturation below 93% and lung involvement covering more than half of both lungs on imaging. These patients often require mechanical ventilation to survive the acute phase.
Cardiovascular Damage
COVID-19 can injure the heart through several pathways: direct viral invasion of heart muscle cells, widespread inflammation, oxygen deprivation, and abnormal blood clotting. Autopsy studies of patients who died from severe COVID-19 have found striking rates of cardiac involvement. In one detailed autopsy series, 90% of deceased patients showed signs of heart muscle inflammation (borderline myocarditis), and nearly 1 in 5 had blood clots in the large or small vessels of the heart.
Pericarditis, inflammation of the sac surrounding the heart, appeared in about 10% of fatal cases. Blood vessel inflammation (vasculitis) was also a recurring finding. These numbers reflect the most severe end of the spectrum, but even people with moderate illness sometimes develop heart palpitations, chest pain, or reduced heart function that takes weeks to resolve.
Effects on the Brain and Nervous System
Neurological symptoms are among the most distinctive features of COVID-19. Loss of smell and taste became an early signature of infection, caused by the virus attacking cells in the nasal lining and tongue where ACE2 receptors are highly concentrated. The tongue’s surface, particularly around the taste buds, has some of the highest ACE2 levels in the oral cavity.
Beyond smell and taste, patients report headaches, dizziness, difficulty concentrating, sleep disruption, and a pins-and-needles sensation in the extremities. The cognitive difficulties often described as “brain fog,” trouble finding words, difficulty focusing, and slowed processing, can persist long after the initial infection clears. These neurological effects likely stem from a combination of direct viral activity, inflammation in blood vessels supplying the brain, and the immune system’s prolonged response.
Mental Health After Infection
COVID-19 takes a measurable toll on mental health. Among people who had mild to moderate infections, roughly 18% developed at least mild depression symptoms afterward, and about 18% experienced anxiety. Post-traumatic stress symptoms appeared in a similar proportion, about 18% of non-severe cases.
People who survived severe COVID-19 fared somewhat worse: around 20% reported depression, 19% had anxiety, and 19% screened positive for PTSD. These rates are significantly higher than background rates in the general population, suggesting the infection itself, not just the stress of being sick, contributes to mental health changes. The biological mechanisms likely include brain inflammation, disrupted sleep, and the lingering effects of oxygen deprivation during acute illness.
Long COVID
For some people, the effects of COVID-19 don’t end when the acute infection resolves. Long COVID refers to symptoms that persist for weeks, months, or even years after the initial illness. More than 200 distinct symptoms have been linked to the condition, but the most commonly reported are fatigue, brain fog, and post-exertional malaise, a hallmark symptom where physical or mental effort triggers a disproportionate crash in energy and function.
The symptom list spans nearly every body system:
- Respiratory and cardiac: shortness of breath, persistent cough, chest pain, heart palpitations
- Neurological: difficulty concentrating, headaches, sleep problems, dizziness on standing, altered smell or taste, depression, anxiety
- Digestive: diarrhea, stomach pain, constipation
- Musculoskeletal and other: joint or muscle pain, rashes, changes in menstrual cycles
The fatigue associated with Long COVID is not ordinary tiredness. It often interferes with daily activities like working, cooking, or even showering, and it doesn’t improve with rest. For many patients, the unpredictability of symptoms is as disabling as the symptoms themselves, with good days followed by sudden setbacks.
Effects in Children
Most children experience mild COVID-19, but a rare complication called Multisystem Inflammatory Syndrome in Children (MIS-C) can develop in the weeks following infection. MIS-C involves widespread inflammation that can affect the heart, digestive system, skin, and blood. Children with MIS-C typically develop a high fever along with symptoms in at least two organ systems: cardiac involvement (reduced heart function, elevated markers of heart stress), skin and mucous membrane changes (rash, red eyes, swollen lips, strawberry tongue), gastrointestinal symptoms (abdominal pain, vomiting, diarrhea), or dangerously low blood pressure.
MIS-C requires hospitalization and can be life-threatening without treatment, but most children recover fully with appropriate care. The condition occurs in people under 21 and is linked to a recent COVID-19 infection or close contact with someone who had it.
Does Vaccination Change the Risk?
Vaccination reduces the severity of acute COVID-19 and appears to lower the risk of developing Long COVID. A review of the available evidence estimated that vaccination reduces Long COVID risk by 40% to 50% on average, though individual studies report reductions ranging from 15% to 70%. However, the picture is not completely settled. At least one large study found that about 7% of patients were diagnosed with Long COVID regardless of vaccination status, with no meaningful difference between unvaccinated people and those who received two or more vaccine doses. Vaccination clearly reduces the chance of severe acute illness and death, but its protective effect against lingering symptoms appears to vary.