What Happens When COVID-19 Attacks the Body

Most cases are mild but more serious infections can lead to deadly complications.

Updated on September 21, 2020 at 11:30am EDT.

The coronavirus that causes COVID-19—SARS-CoV-2—was first identified in Wuhan, China in late 2019. Since then, it’s spread to at least 188 countries, infected more than 31 million people and claimed more than 960,000 lives around the world.

More than 80 percent of those with COVID-19 develop only a mild to moderate infection and recover without the need for hospitalization, the World Health Organization estimates. Roughly 15 percent of cases result in severe illness and complications, including pneumonia and trouble breathing. Another 5 percent, will develop very serious issues, including respiratory failure, septic shock and organ failure.

Here’s what happens to the body when Sars-CoV-2 invades:

Early signs and symptoms
Symptoms of COVID-19 may appear anywhere from 2 to 14 days after exposure to the novel coronavirus, according to the Centers for Disease Control and Prevention (CDC). The WHO reports that in some cases, the incubation period may be even longer than 14 days.

Those infected with COVID-19 have developed a range of symptoms associated with a respiratory infection, including:

  • Fever
  • Dry cough
  • Fatigue
  • Loss of sense of smell
  • Phlegm or a productive cough
  • Shortness of breath
  • Sore throat
  • Headache
  • Muscle and joint pain
  • Chills

People with COVID-19 could even mistake their symptoms for the flu or a common cold. That’s why laboratory tests are needed to confirm the diagnosis.

Digestive symptoms—diarrhea, loss of appetite, nausea and vomiting—are also commonly reported among COVID-19 patients. Some evidence suggests that certain COVID-19 patients may only develop these digestive symptoms and not experience fever or any respiratory symptoms. Researchers in China also found that those with digestive symptoms took longer to clear the virus from their systems.

Exactly how COVID-19 affects the digestive system is still under investigation but these findings could suggest that many people with mild infections and digestive symptoms, which they may not readily associate with COVID-19, may be unknowingly spreading the novel coronavirus to others.

You can track the duration and severity of your symptoms by using the symptom tracker tool on the Sharecare app.

How some infections become deadly
More severe coronavirus infections could lead to pneumonia. This occurs when the infection triggers inflammation in the lungs' air sacs (alveoli), causing them to fill up with fluid.

When this happens, breathing becomes more difficult, which prevents oxygen from reaching the blood. People with pneumonia may also develop severe coughing along with fever and chills.

In extreme cases, COVID-19 can lead to acute respiratory distress syndrome (ARDS) and death from respiratory failure. COVID-19 is just one risk factor for ARDS. The condition can also result from trauma, other infections, breathing in dangerous chemicals and other lung injuries.

Early on in ARDS, fluid from tiny blood vessels in the lungs begin to leak into the alveoli. The lungs become stiffer and their capacity becomes progressively smaller, which makes it increasingly difficult to breathe. Since oxygen isn’t moving from the lungs to the blood as well, the amount of oxygen in the bloodstream drops. When the rest of the body isn’t getting the oxygen its needs, the brain, heart and other vital organs can be damaged or fail.

COVID-19 could also lead to shock and acute kidney injury or kidney failure, according to the CDC. It’s the job of the kidneys to filter waste products from the body, help produce red blood cells and regulate blood pressure. Those with kidney failure have lost 85 to 90 percent of their kidney function, which is insufficient to sustain life without treatment.

Oxygen supplementation and ventilators, which are in short supply, are essential for those with severe cases of COVID-19. This life-saving support can help the body get the oxygen it needs until the lungs are able to recover.

COVID-19 may also attack the heart
COVID-19 is a respiratory disease but ongoing research suggest that it could also lead to heart-related problems.

Scientists gathering data from China, Italy, New York and other hot spots around the world suspect that the novel coronavirus may infect the heart muscle. One March 25 study from China published in JAMA Cardiology involving 416 patients sick enough to be hospitalized found that 20 percent had signs of heart damage.

Of these patients, 51 percent died from the infection, suggesting the risk of death may be higher for those with heart damage—even among those who didn’t have heart disease before they developed COVID-19.

Who is at higher risk for serious complications?
Anyone can develop COVID-19 but older people seem to be among those at highest risk for serious disease. The immune system weakens with age and older people are more likely to have underlying health issues, such as diabetes and heart disease, which also increase the risk for COVID-19-related complications.

It’s important to note that some 40 percent of U.S. patients sick enough to be hospitalized were between 20 and 54-years old, the CDC reported as of March 26. The risk of dying, however, is much greater for older people.

Children, on the other hand, appear to be less likely to develop serious illness, the WHO points out. Scientists are still working to understand why this may be the case.

How to protect yourself
Unlike the seasonal flu, measles or other vaccine-preventable diseases, there are no immunizations that help protect against coronaviruses. Since this is a new coronavirus, humans have not developed any natural immunity to it as they have against many other infections.

But there are steps you can take to reduce your risk of infection or potentially spreading the novel coronavirus on to others.

One of the best ways to help is to just stay home and go out in public only when necessary. If you do leave home, practice social distancing—keep at least six feet of space between you and others.

U.S. and state health officials are also advising Americans—whether they have symptoms or not—to wear nonmedical coverings, such as scarves or cloth masks, over their noses and mouths when going out to help “flatten the curve.” 

Other ways to help curb the spread of COVID-19:

  • Wash your hands well and often with soap and water for at least 20 seconds each time.
  • Avoid touching any part of your face, including your eyes, nose or mouth with unwashed hands.
  • Cover your cough or sneeze with an unused tissue, then throw the tissue in the trash. If you don’t have a tissue, use your upper sleeve or elbow—not your hands.
  • Clean and disinfect commonly used objects and surfaces you come into contact with throughout your day, such as computer keyboards, cell phones, doorknobs, faucets and bathroom fixtures with household cleaning sprays or wipes. Effective products include diluted household bleach solutions or cleaners with at least 70 percent alcohol as well as most common EPA-registered household disinfectants.

If you think you’re infected
If you believe you were exposed to COVID-19 or if you, or someone in your home, has symptoms consistent with a respiratory infection, don’t panic. 

Instead, take immediate steps to isolate yourself to avoid spreading your illness to others. This means keeping distance between yourself and the other people in your home. Call your healthcare provider (HCP) for instructions. Do not go to your doctor’s office without calling ahead first and letting the office staff know that you suspect you’ve been exposed to COVID-19.

Your doctor should determine if you can be treated at home, and also determine if you should be tested for the coronavirus and where that should be done.

If you develop serious warning signs of COVID-19, however, you need to seek immediate medical attention. These red flags may include:

  • Difficulty breathing or shortness of breath
  • Persistent pain or pressure in the chest
  • Feeling confused
  • Bluish lips or face

Call 911 and let the operator know that you have or think you may have COVID-19. If you have a medical mask, put it on before help arrives.

Medically reviewed in April 2020.

Johns Hopkins University. “The Center for Systems Science and Engineering (CSSE). Coronavirus COVID-19 Global Cases
Centers for Disease Control and Prevention. “SARS Basics Fact Sheet.”
World Health Organization. “WHO Director-General's remarks at the media briefing on COVID-2019 outbreak on 17 February 2020.”
World Health Organization. “Middle East respiratory syndrome coronavirus (MERS-CoV).”
World Health Organization. “Coronavirus disease (COVID-19) advice for the public: Myth busters.”
World Health Organization. “Q&A on coronaviruses.”
Centers for Disease Control and Prevention. “Coronavirus Disease 2019 (COVID-19).”
American Lung Association. “Learn About Pneumonia.”
National Kidney Foundation. “What is Kidney Failure?”
Centers for Disease Control and Prevention. “What to Do if You Are Sick.”
Han C, et al. "Digestive Symptoms in COVID-19 Patients with Mild Disease Severity: Clinical Presentation, Stool Viral RNA Testing, and Outcomes." The American Journal of Gastroenterology. 2020.
American Lung Association. “Learn About ARDS.”
Centers for Disease Control and Prevention. “Severe Outcomes Among Patients with Coronavirus Disease 2019 (COVID-19) — United States, February 12–March 16, 2020.”
S. Shi, M. Qin, B. Shen, et al. “Association of Cardiac Injury With Mortality in Hospitalized Patients With COVID-19 in Wuhan, China.” JAMA Cardiology. Published online March 25, 2020.

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