Updated on July 11, 2024.
The coronavirus that causes COVID-19 was first identified in Wuhan, China in late 2019. As of summer 2024, it’s claimed 1.2 million lives in the United States and over 7 million lives worldwide, according to the World Health Organization (WHO). Exponentially more people have been infected with the virus than have died from it.
Most people with COVID-19 develop only a mild to moderate infection and recover without the need for hospitalization. Some people, however, experience severe illness and complications, including pneumonia and trouble breathing. Another small percentage of people will develop very serious issues, including respiratory failure, septic shock, and organ failure.
The good news is that vaccinations for COVID-19 are free in the United States. They’re also safe and effective. The Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months or older should stay updated on their COVID-19 vaccines. Vaccines don’t always prevent a person from becoming infected, but they do help the body’s immune response. That means most vaccinated people will have much milder symptoms than if they hadn’t been vaccinated.
Here’s what happens to the body when you have COVID-19.
Early signs and symptoms
Symptoms of COVID-19 may appear anywhere from 2 to 14 days after exposure to SARS-CoV-2 (the virus that causes COVID-19), according to the CDC. Those infected with COVID-19 may develop any of a range of symptoms associated with a respiratory infection, including:
- Fever
- Cough
- Loss of sense of smell or taste
- Shortness of breath
- Fatigue
- Sore throat
- Headache
- Muscle and body aches
- Runny nose or congestion
- Diarrhea
- Nausea or vomiting
This list doesn’t include every possible symptom, nor does it include symptoms that can come a bit later or be more long-lasting. (See the section below on how COVID-19 affects the brain, heart, and other systems.) Each person may respond to the virus differently, and each variant of the virus may affect the body differently.
Still, the initial symptoms of COVID-19 tend to be similar to those of other conditions. As a result, people with COVID-19 might mistake their symptoms for the flu or a common cold. That’s why COVID-19 tests are important for confirming the diagnosis.
How COVID can affect the lungs and become deadly
COVID-19 infections that are more severe could lead to a type of pneumonia called bilateral interstitial pneumonia. The word bilateral refers to having pneumonia in both lungs at the same time, rather than just one. The word interstitial refers to the tissue around and between the lungs’ air sacs (or alveoli), airways, and blood vessels, which can get damaged or scarred from inflammation.
This type of pneumonia usually arises after the phase of disease that comes immediately after being infected with COVID. But sometimes people who get “long COVID” will develop this type of pneumonia.
With bilateral interstitial pneumonia, breathing becomes more difficult, which reduces the amount of oxygen that can reach the blood. Sometimes this pneumonia is caused directly by COVID-19-induced inflammation, and sometimes pneumonia can come about because the immune system, weakened by the virus, allows bacteria to infect the lungs as well.
The main difference between COVID-related pneumonia and other types of pneumonia is that COVID pneumonia moves more slowly through the lungs. This means it sticks around longer and can do more damage. Other types of pneumonia tend to sweep through the lungs more quickly.
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 begins 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 effectively, 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.
Oxygen supplementation and ventilators are often 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.
If a person with COVID-19 shows any of these warning signs, it’s important to take them to the nearest emergency department (ED) right away:
- Difficulty breathing
- Confusion
- Chest pressure or pain
- Trouble waking or staying awake
- Discolored skin, lips, or nail beds (usually pale, gray, or blue-colored, depending on a person’s natural skin tone)
COVID-19 can also affect the brain, heart, and other organs
COVID-19 is not just a respiratory disease. Ongoing research has shown that it can cause problems throughout the body, especially within the cardiovascular (heart and blood vessels) system and nerve endings. It does this by revving up the immune system so much that the entire body can experience harmful inflammation and blood clots.
Heart
COVID-19 can lead to irregular heartbeats and myocarditis (inflammation of the heart). It can also raise the risk of deep vein thrombosis and pulmonary embolisms. (These conditions occur when blood clots form in veins deep within the body, such as in the legs, then break off and block blood flow in the arteries of the lungs.)
According to the American Heart Association, there is some evidence that micro-clots (small blood clots) may cause issues in the muscle cells of the heart. Inflammation may also lead plaque in the coronary arteries to break off and cause a heart attack. (Coronary arteries are those that supply blood to the heart muscle.)
Brain
While the reasons are not yet understood fully, the brain may be affected by COVID. This isn’t because the virus itself is harming the brain tissue. Instead, it’s the immune system’s response that causes the issues.
Some people with COVID-19 report “brain fog” that can last for months, even after a very mild infection. Migraines as well as numbness and tingling in the legs and arms are also possible.
Gastrointestinal system
COVID-19 can wreak havoc in your stomach, colon, and intestines, too. It seems that the virus finds the intestinal tract to be an excellent hiding place, so it can stay there even when the rest of the body has cleared the virus. This can cause nausea, diarrhea, and vomiting. It might also raise the risk of gastroesophageal reflux disease (GERD) and irritable bowel syndrome (IBS), even if the original COVID-19 infection was mild.
Kidneys
A COVID-19 infection can cause damage to the kidneys, too, though researchers aren’t yet sure about the reasons. It might be that because people are sick, they lose a lot of fluids that aren’t replenished. Or it could be similar to other systems in the body, where inflammation causes organ damage.
It’s the job of the kidneys to filter waste products from the body, to help produce red blood cells, and to regulate blood pressure. People with kidney failure are those who have lost 85 to 90 percent of their kidney function. They are particularly vulnerable to the effects of COVID-19.
Long COVID
For some people, symptoms of COVID-19 infection can last a long time. Long COVID, also called post-COVID-19 syndrome or long-haul COVID-19, can cause ongoing or returning symptoms for months or years. It can even cause people to become disabled. The most common symptoms of long COVID include:
- Fatigue
- Fever
- Trouble breathing
- Cough
- Symptoms that worsen after straining physically or mentally
Less common long COVID symptoms can include the issues listed above (damage to the heart, brain, gastrointestinal system, and kidneys) as well as:
- Trouble thinking or concentrating
- Difficulty sleeping
- Dizziness when standing
- Tingling sensations
- Loss of smell
- Depression and anxiety
- Changes to the menstrual cycle
- Rashes
It can sometimes be difficult to discern the causes of symptoms experienced after an initial COVID-19 infection. Some symptoms could be from other chronic illnesses, like chronic fatigue syndrome, which may develop after a person has had a viral infection. A healthcare provider (HCP) can talk with you and do lab tests and other procedures to help figure out the root of long-term symptoms. Doing so can point the way to the best treatments for you.
Reinfection with COVID-19
Even if you’ve had COVID-19 before, and even if you’re vaccinated, you can still get infected with the virus multiple times. Reinfections are usually milder cases, especially for people who are up-to-date on their vaccinations. But sometimes reinfections can be more severe—even if previous infections were mild.
When a person with a healthy immune system gets COVID-19, their immune response can offer protection for a few months, but the protective effect lessens over time. People with immune systems that have been weakened by other conditions may not get much, or any, protective effect after being infected.
The coronavirus is also changing and evolving, with new variants finding ways around the immune system’s protective measures. That makes it essential to stay up-to-date on the latest versions of the COVID vaccine.
Who is at high risk for serious complications?
Anyone can develop COVID-19. But some people are at particular risk for severe symptoms or serious complications. There are a set of known risk factors that, especially if combined, can come together to raise the overall risk of serious illness from the virus.
People over age 65
People over age 65 are at higher risk of needing hospital care for a COVID-19 infection. As people age, their immune systems can become less effective. Also, older people are more likely to have another medical condition that can raise the risk of serious illness.
According to the CDC, about 22 percent of deaths from COVID-19 have been among people ages 65 to74. The risk goes up as a person ages, with 54 percent of deaths from COVID-19 being from people ages 75 and older.
Infants
Infants 6 months old or younger are also at higher risk of serious illness. This age group is still developing their immune systems and they’re also not able to be receive COVID-19 vaccines.
People with other health conditions
The risk of a more severe case of COVID-19 rises if you have certain other health issues, including:
- Heart disease
- Obesity
- Chronic kidney disease
- Diabetes
- Chronic lung diseases, including moderate to severe asthma, tuberculosis, chronic obstructive pulmonary disease (COPD), cystic fibrosis, and interstitial lung disease
- Cancer, with blood cancer raising the risk more than tumor-based cancers
- Strokes
- Chronic liver diseases
- HIV that isn’t being managed well with medications
- Mood disorders and schizophrenia
- Sickle cell anemia
- Dementia
- Cerebral palsy
- Being an organ or stem cell transplant recipient
Pregnant people or those who’ve recently given birth, people with Down syndrome, and those with attention deficit/hyperactivity disorder (ADHD) may also be at higher risk of needing hospital care.
Other risk factors
Lifestyle and medications can affect your risk level, as well. People who aren’t physically active, people who smoke, and those who take medications that lower the immune system are all at risk of more severe COVID-19.
The Cleveland Clinic has an online hospitalization risk calculator that offers a general idea of your risk of hospitalization if you get COVID-19. Using basic information including your sex, age, BMI, and whether you’re a smoker or have other health issues, it can offer a risk percentage.
How COVID-19 affects children
In most kids and adolescents over 6 months of age, COVID-19 infections have few or no symptoms. But some children with other medical conditions or special healthcare needs are at a greater risk of severe disease.
These include kids with genetic, neurologic, or metabolic diseases as well as the same conditions that raise adults’ risk, such as obesity, asthma, diabetes, chronic lung disease, sickle cell disease, or those receiving immunosuppression treatments.
It’s very rare, but some children who’ve been infected with the SARS-CoV-2 virus develop a complication called Multisystem Inflammatory Syndrome in Children (MIS-C). (Adults can get it, too. In adults it’s just called MIS.)
With MIS-C, about two to six weeks after having a COVID-19 infection, a child’s body becomes inflamed in one or more of many areas, including the heart, brain, skin, eyes, lungs, kidneys, and gastrointestinal tract.
Initial signs of MIS-C include having a fever that doesn’t go away, along with another symptom such as a skin rash, bloodshot eyes, dizziness, stomach pain, diarrhea, and vomiting.
Severe symptoms include confusion, trouble breathing, persistent chest pressure or pain, intense abdominal pain, being unable to wake up or stay awake, and having discolored lips, skin, or nail beds (pale, gray, or blue, depending on a child’s skin tone). If your child has these symptoms make sure to take them to the nearest ED.
MIS-C is quite rare, but when it does happen, it doesn’t seem to make a difference whether or not the child had symptoms with their COVID-19 infection. Most kids with MIS-C are otherwise healthy, without any other serious health conditions, though obesity may raise the risk.
There is some good news: Kids with MIS-C that affects their heart seem to get better rapidly in most cases. Vaccination can also help lower the risk of MIS-C even further.
How to protect yourself
There are three highly effective ways to protect yourself from COVID-19.
Vaccination
The most important protective measure you can take against a COVID-19 infection is to stay up-to-date on your COVID-19 vaccines. Although a vaccine can’t stop all disease, getting the latest vaccine means your risks of severe illness, hospitalization, or death are greatly lowered. Vaccination also lowers the risk of having symptoms of long COVID.
Hygiene
Practicing good hygiene is an important part of avoiding getting or spreading respiratory illnesses. This means doing the following:
- Cover your sneezes and coughs with a tissue or use your elbow
- Wash your hands often with soap and water or use a hand sanitizer with 60 percent alcohol or higher
- Clean surfaces that are frequently touched, like door handles, countertops, and faucets
Clean air
Since the SARS-CoV-2 virus can spread in places where air is not circulating well, you can protect yourself by cleaning the air or making sure there’s a supply of fresh air. Incorporate these habits into your daily life for cleaner air:
- Keep windows and doors open whenever you’re able
- Meet with others outdoors whenever possible
- Use filters with pleats in your central heating, ventilation, and air conditioning (HVAC) system, if you have one. Turn the fan to “on” rather than “auto” when you’ll be having guests. Make sure to follow the manufacturer’s guidance about how often you should replace the filter.
- If you’re able to, use a portable high-efficiency particulate air (HEPA) purifier.
It’s also important to protect not just yourself but others. If you have reason to believe you might have COVID-19 because of respiratory symptoms or a positive COVID-19 test, stay away from others until you’ve recovered. According to the CDC, you can return to normal activities when, for a minimum of 24 hours, your symptoms have been improving and you’ve not had a fever without the use of any fever-reducing medication for the previous 24 hours.
Still, when you go back to your activities and you are around other people, keep in mind you might still be contagious. It’s important to continue to practice good hygiene and try to ensure fresh or filtered air. You should also wear a mask to reduce the spread of the virus. Opt for the mask that offers the most protection and make sure it fits snugly.
Finally, practice physical distancing if you’re ill or if you are around others who may be ill or have been exposed. While early on in the COVID-19 pandemic, staying at least 6 feet away was a common recommendation, now the CDC simply recommends keeping as much of a distance as you can and avoiding crowded spaces.
What to do 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 (but you don’t have symptoms that require a trip to the ED), it’s helpful to first isolate yourself to avoid spreading your illness to others. This means keeping distance between yourself and the other people in your home.
Next, it’s important to take a COVID-19 test. There are several at-home tests, and most HCPs also offer tests for influenza to determine what’s causing your symptoms.
Consult with your HCP for guidance on your treatment. There are antiviral treatments available which may shorten how long you’re sick and make your symptoms less severe if you are at high risk of serious illness. These treatments can also lower the risk of being hospitalized.
If you develop serious warning signs of COVID-19, such as difficulty breathing, confusion, discolored lips and nailbeds, or chest pain or pressure, you need to seek immediate medical attention. Call 911 or get to the nearest ED.
