COVID-19 (coronavirus disease 2019) is a respiratory illness caused by the SARS-CoV-2 virus. It is very contagious, and spreads quickly.
Most people with COVID-19 have mild respiratory symptoms that feel much like a cold or flu. But it can be much more serious for older adults, people with underlying medical conditions, and those who haven’t been vaccinated against COVID-19. Some people may go on to suffer from post-COVID conditions, known as “long COVID.” Mounting evidence suggests that COVID vaccines protect against long COVID.
Vaccines against COVID-19 are the best defense against the virus, as they protect against serious disease, hospitalization, and death.
Even if you have been vaccinated, you will want to take steps to reduce your chances of infection. That may mean temporarily wearing masks indoors or avoiding large gatherings if COVID-19 levels are high in your area. The good news is these steps will also reduce your risk of developing other respiratory viruses, like colds or flus, too.
We know a lot more about COVD-19 than we did in 2020, and yet we’re still learning. We will continue to provide important updates.
Respiratory viruses spread from person to person through the tiny droplets that sick people propel when they cough, sneeze, or talk. These droplets, known scientifically as infectious respiratory particles, can fly six feet or more in the air, and they can spread the virus if they deposit on someone’s mouth or nose, or get inhaled into a person’s lungs. The COVID-19 virus can remain suspended in the air for a period of time and drifting farther than six feet, which is why mask wearing can help prevent spread of the virus.
In the case of coronavirus, an infected person doesn’t need to show symptoms to spread the virus. After people are infected, they may have no symptoms for several days, or for the duration of their illness. Even if they are asymptomatic, they can still spread the virus.
Age, weight, and underlying conditions all play a role.
Several factors increase a person’s chance of having a more severe case of COVID-19. They include the following:
Spot key distinctions with this guide.
Symptoms of colds, flu, and COVID-19 can overlap, so it can be hard to tell which one you have. The only way to know for sure is to get tested for both the flu and COVID-19. But there are some differences between all three.
| SYMPTOM | COVID-19 | FLU | COLD |
|---|---|---|---|
| Fever | Less common now, but can be high (100° to 103° F) | Common and often high (100° to 103° F) | Rare |
| Headache | Can occur | Often and can be severe | Rare |
| General aches and pains | Can occur | Often severe | Slight |
| Fatigue | Can occur and may be intense | Can last two to three weeks | Mild |
| Stuffy nose, sneezing | Sometimes | Sometimes | Common |
| Sore throat | Sometimes | Common | Common |
| Cough | Common, can be severe | Common, can be severe | Mild to moderate |
| Loss of smell | One of the more common symptoms | Sometimes partial and temporary | Sometimes partial and temporary |
| Vomiting, diarrhea | Sometimes | Sometimes | Rare |
| Shortness of breath | Less common now, but can occur with more serious infections | Rare (unless complicated by pneumonia) | Rare |
Source: National Institute of Allergy and Infectious Diseases; FDA.
It can be hard to know based on symptoms alone.
Two types of tests are used to confirm a diagnosis of an active coronavirus infection.
PCR tests detect the presence of the virus’s genetic material using a technique called reverse transcriptase polymerase chain reaction, or RT-PCR. For the PCR test, the sample is typically sent to a laboratory where coronavirus RNA (if present) is extracted from the sample and converted into DNA. The DNA is then amplified, meaning that many copies are made in order to produce a measurable result. PCR tests are highly accurate. However, it can take days to over a week to get the results.
Antigen tests detect specific proteins on the surface of the coronavirus. Most authorized at-home over-the-counter COVID-19 tests are antigen tests. They are sometimes referred to as rapid diagnostic tests because the results can be back within 15 minutes. If you test positive, you are very likely to be infected. However, there is a higher chance of false negatives with antigen tests, which means that you could test negative and still have an active infection. If you’ve taken a COVID-19 antigen diagnostic test at home, you should repeat testing 48 hours after a negative result to reduce your risk of a false negative.
If you test positive for COVID-19, the CDC recommends that you stay home and away from others until you have experienced both of the following for at least 24 hours:
The CDC recommends taking additional steps, such as masking, washing hands more often, and keeping a distance from others, for five days after resuming normal activities.
While most cases are mild, the illness can cause bodywide complications.
Most people who are infected with the virus that causes COVID-19 have no symptoms or mild symptoms. Yet in some people — particularly older adults, those with underlying medical conditions, and the unvaccinated — the illness triggers an intense immune system reaction that can cause bodywide complications like these:
Even after release from the hospital, recovery may be slow, with rehabilitation sometimes needed after discharge and a variety of effects lingering for months, perhaps longer.
In general, the virus is milder in children, but in a small number of children it causes the immune system to overreact and produce bodywide inflammation. In a few cases, this syndrome has proved deadly.
Some people who have been infected with the virus that causes COVID-19 go on to develop long COVID, where symptoms persist for more than four weeks after the original infection. It’s not clear how many people go on to develop long COVID, since there are many undocumented cases, but it’s estimated to be about 18% among adults in the U.S. Symptoms may include:
Researchers still don’t understand fully who is more likely to develop long COVID. You’re thought to be more at risk if you were hospitalized for COVID, have underlying health conditions, or never got a COVID-19 vaccine.
Some general steps can help keep you healthy.
You can take steps to reduce exposure to COVID-19.
Stay up to date with COVID vaccines. Vaccines are the best defense against the virus. They protect against serious disease, hospitalization, and death.
Improve ventilation. When gathering with others, open windows to bring in as much outside air as possible. Consider also moving indoor activities outdoors.
Avoid contact with anyone who has tested positive for COVID-19. Separate yourself from anyone you know who has tested positive for COVID-19 — whether or not they are symptomatic — until they test negative.
Wearing masks. Masks can reduce the number of germs you breathe in or out. The CDC recommends wearing a mask for five days once you’ve resumed normal activities after recovering from COVID-19. You can also consider wearing a mask if you or someone in your household is at high risk for getting very sick from COVID-19.
Handwashing. Wash your hands often with soap and water for at least 20 seconds, especially after going to the bathroom; before eating; after blowing your nose, coughing, or sneezing; and after handling something that’s come from outside your home.
General health tips. Here are other ways to avoid getting — and spreading — the germs that cause COVID-19:
Here’s how to keep your immune system healthy and primed for attack.
Your immune system is your body’s defense system. When a harmful microorganism — like the virus that causes COVID-19 — gets into your body, your immune system mounts an attack. Known as an immune response, this attack is a sequence of events that involves various cells and unfolds over time.
Following general health guidelines is the best step you can take to keep your immune system strong and healthy. Every part of your body, including your immune system, functions better when protected from environmental assaults and bolstered by healthy-living strategies such as these:
Three COVID-19 vaccines, developed by Pfizer/BioNTech, Moderna, and Novavax, are currently available in the United States. They were developed in the fall of 2023 for the 2023–2024 COVID-19 season. All three vaccines are monovalent and protect against the XBB.1.5 COVID-19 variant. The Pfizer/BioNTech and Moderna vaccines are mRNA vaccines. The Novavax vaccine is not an mRNA vaccine.
Updated vaccines from Pfizer/BioNTech, Moderna, and Novavax for the 2024–2025 season are expected to be available in fall 2024. The updated vaccines will be monovalent and will target the KP.2 strain of the JN.1 virus lineage. The CDC recommends that everyone ages 6 months and older receive an updated 2024–2025 COVID-19 vaccine once they are available.
Older (original and bivalent) COVID-19 vaccines are no longer authorized for use in the United States.
Protection from the COVID-19 vaccine wanes over time. How long protection lasts depends on many factors including age, underlying medical conditions, and previous infection.
Everyone six months and older should get one currently available (2023–2024) COVID-19 vaccine, regardless of whether they’ve previously received any COVID vaccines, in order to be up to date with their COVID vaccines.
For now, the CDC only recommends an additional dose of the currently available COVID-19 vaccine for people who are moderately or severely immunocompromised. Talk to your healthcare provider if you fall into this category.
mRNA, or messenger RNA, is genetic material that contains instructions for making proteins. mRNA vaccines for COVID-19 contain synthetic mRNA. Inside the body, the mRNA enters human cells and instructs them to produce the “spike” protein found on the surface of SARS-CoV-2, the virus that causes COVID-19. The body recognizes the spike protein as an invader and starts producing antibodies against it. Soon after, the cell breaks down the mRNA into harmless pieces. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness. An mRNA vaccine cannot change your DNA.
The two mRNA vaccines available in the US are made by Pfizer/BioNTech and Moderna.
There are only a few groups of people who should not get the mRNA vaccine. They include people who
If you have a history of allergic reactions to other (non-COVID) vaccines or to injectable medications, talk to your doctor about the risks and benefits of getting an mRNA vaccine.
There has a been a higher-than-expected number of heart inflammation cases after vaccination with the mRNA COVID-19 vaccines, particularly among boys and young men.
Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the outer lining of the heart) after vaccination were most common in males ages 16 to 24. Cases tended to occur within several days after the second mRNA vaccine dose. Most people who developed myocarditis or pericarditis had mild cases and recovered completely after treatment.
The CDC still recommends that everyone ages 6 months and older get vaccinated for COVID-19. That’s because the known risks of COVID-19 illness and its possibly severe complications — such as long-term health problems, hospitalization, and even death — far outweigh the possible risks of vaccination.
Rest, fluids, and certain medications are key.
The CDC advises everyone with mild COVID-19 illness to stay home and rest. Get plenty of fluids and manage symptoms with over-the-counter medications like acetaminophen (Tylenol).
Call your doctor right away if you have severe symptoms like trouble breathing, chest pain, or a high fever that doesn’t go away.
If you’re at higher risk to develop complications from COVID-19 — for example, you’re over the age of 50, have lung or heart disease, or have a weakened immune system — there are antiviral treatments available to reduce your risk of severe disease. You must begin within a few days after the start of symptoms, so call your doctor as soon as you test positive or begin feeling ill.
Antiviral treatments
Antiviral medicines target specific parts of the virus that causes COVID-19, to stop it from multiplying in the body.
Antiviral treatments for COVID-19 include
These drugs can help reduce risk of hospitalization and death. They have, however, been linked to “COVID rebound,” where people recover, then develop COVID symptoms again a few days later. People who have not taken Paxlovid can also experience a return of symptoms, and the evidence is mixed on the degree to which Paxlovid contributes to the “rebound” effect.
When to seek emergency care
Seek a doctor’s advice if symptoms are severe or getting worse.
Call 911 or go to a hospital if you have emergency symptoms like these:
If you have a severe case and are having trouble breathing, you may need care in a hospital. There you’ll get oxygen, fluids, and other supportive treatments to manage your symptoms. You may also receive the following drugs:
Remdesivir. This drug is recommended for adults and children hospitalized with COVID, whether or not they require supplemental oxygen. There’s some evidence that it can shorten the recovery time.
Dexamethasone. The corticosteroid drug dexamethasone is often used in conjunction with remdesivir among patients who require oxygen. It has been shown to shorten hospital stays for people severely ill with COVID, and perhaps prevent them from needing to go on a ventilator.
Other immune-inhibiting drugs. Either baricitinib or tocilizumab may be given to people in the hospital who need increased oxygen support despite treatment with dexamethasone. Each of these drugs suppresses a different pathway in the body’s immune response.
COVID is generally mild in children, but can cause a serious complication.
Children, including very young children, can develop COVID-19. Many of them have no symptoms. Those that do get sick tend to experience milder symptoms such as low-grade fever, fatigue, and cough. Some children have more severe complications of COVID-19, but this is less common. Children with underlying health conditions may be at increased risk for severe illness.
A potentially severe and dangerous complication can occur in children. Called multisystem inflammatory syndrome in children (MIS-C), it can lead to life-threatening problems with the heart and other organs in the body. In this condition, different body parts, such as the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal organs, can become inflamed. Being vaccinated helps protect children from MIS-C.
Symptoms of MIS-C can include
Many conditions can cause symptoms similar to those of MIS-C.
Call your doctor right away if you suspect your child has COVID and also has symptoms like these:
Call 911 or take your child to the emergency room for symptoms like these:
Kids with mild symptoms can be treated at home.
Certain groups of people are more vulnerable.
Certain groups of people are more likely to develop complications from COVID-19. Here’s why, and how to stay protected.
Older adults
People ages 65 and older are at increased risk for a severe COVID infection, especially those with underlying medical conditions like heart or lung disease or diabetes. It’s very important to stay up to date on your COVID-19 vaccines. If you do develop COVID-19, talk to your doctor about antiviral treatments, which can help reduce risk of complications.
People with chronic illnesses
It’s especially important for anyone with a chronic health condition to stay up to date on their COVID vaccines. People with the following conditions are at higher risk of getting very sick from the virus, especially if their disease isn’t well controlled:
Pregnancy
The CDC recommends that women who are pregnant, breastfeeding, trying to get pregnant, or might become pregnant in the future should stay up to date with their COVID-19 vaccines.
Here are some factors to consider. First, although the actual risk of severe COVID-19 illness and death among pregnant individuals is very low, it is higher when compared to nonpregnant individuals from the same age group. In addition, COVID-19 increases risk for premature birth, stillbirth, and possibly also for other undesirable pregnancy outcomes.
Evidence shows that COVID vaccination during pregnancy is safe for mother and baby. In addition, vaccine-generated antibodies pass from mother to baby and protect newborns for several months after birth. Protective antibodies are particularly important for infants because COVID vaccines are not authorized for babies younger than 6 months.
Similar to any decision regarding medications during pregnancy, your own doctor is in the best position to advise you based on your personal health risks and preferences.
antibodies: proteins made by the immune system to fight infections. If the antibodies later encounter the same infection, they help prevent illness by recognizing the microbe and preventing it from entering cells.
antigen: a substance displayed on the surface of a microbe that stimulates the body to produce an immune response.
antigen test: a diagnostic test that detects specific proteins on the surface of the virus.
diagnostic test: indicates whether you are currently infected with COVID-19.
epidemic: a disease outbreak in a community or region.
false negative: a test result that mistakenly indicates you are not infected when you are.
false positive: a test result that mistakenly indicates you are infected when you are not.
immunity: partial or complete protection from a specific infection because a person has either had that infection previously or has been vaccinated against it.
incubation period: the period of time between exposure to an infection and when symptoms begin.
infectious respiratory particles: droplets containing respiratory pathogens that can spread from person to person when a sick person coughs, sneezes, or talks.
isolation: the separation of people with a contagious disease from people who are not sick.
long COVID: the constellation of symptoms experienced by COVID long-haulers. These symptoms may include brain fog, shortness of breath, chills, body ache, headache, joint pain, chest pain, cough, and lingering loss of taste or smell.
long-haulers: people who have not fully recovered from COVID-19 weeks or even months after first experiencing symptoms.
mutation: A change to a virus’s genetic material that occurs when the virus is replicating. The change is passed on to future generations of the virus.
mRNA: short for messenger ribonucleic acid, mRNA is genetic material that contains instructions for making proteins.
mRNA vaccines: mRNA vaccines for COVID-19 contain synthetic mRNA. Inside the body, the mRNA enters human cells and instructs them to produce the “spike” protein found on the surface of the COVID-19 virus. The body recognizes the spike protein as an invader, and produces antibodies against it. If the antibodies later encounter the actual virus, they are ready to recognize and destroy it before it causes illness.
pandemic: a disease outbreak affecting large populations or a whole region, country, or continent
polymerase chain reaction (PCR) test: a diagnostic test that detects the presence of the virus’s genetic material.
SARS-CoV-2: short for severe acute respiratory syndrome coronavirus 2, SARS-CoV-2 is the official name for the virus responsible for COVID-19.
spike protein: a protein on the surface of the SARS-CoV-2 virus that binds to and allows the virus to enter human cells.
variant: A virus containing one or more mutations that make it different from a version of the virus that has been circulating.
virus: a virus is the smallest of infectious microbes, smaller than bacteria or fungi. A virus consists of a small piece of genetic material (DNA or RNA) surrounded by a protein shell. Viruses cannot survive without a living cell in which to reproduce. Once a virus enters a living cell (the host cell) and takes over a cell’s inner workings, the cell cannot carry out its normal life-sustaining tasks. The host cell becomes a virus manufacturing plant, making viral parts that then reassemble into whole viruses and go on to infect other cells. Eventually, the host cell dies.
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