Coronavirus disease 2019 (COVID-19) and seasonal flu are illnesses caused by viruses. They can spread from one person to another. Some of the symptoms of COVID-19 and the flu, also called influenza, are the same.

But COVID-19 and seasonal flu are not the same thing. Different viruses cause them. Each illness has its own treatment. And each illness can lead to different problems after recovery. You can get vaccines to help prevent serious COVID-19 and seasonal flu illnesses. But the COVID-19 vaccine and the flu vaccine are two different vaccines.

Viruses cause both COVID-19 and the flu. COVID-19 is caused by SARS-CoV-2, also known as severe acute respiratory syndrome coronavirus 2. The flu is caused by influenza viruses.

COVID-19 and the flu spread when people are close to each other. Both viruses spread better when people are in a space with poor airflow.

When someone with COVID-19 or the flu talks, sneezes or coughs, the virus can get into the air. You can breathe in the virus, or it can get into your mouth or nose.

COVID-19 or flu virus also may land on a surface. You can get sick if you touch something with the virus on it, then touch your mouth, nose or eyes. But this may not happen very often with the virus that causes COVID-19.

COVID-19 may be able to spread from a person for a longer time than seasonal flu. If you have COVID-19, you're more likely to lose your sense of taste or smell.

Both COVID-19 and the flu make millions of people sick each year. The number of people who need to go to the hospital for flu or COVID-19 depends on a person's health and age. It also depends on the specific virus that's spreading and how many people got the vaccine.

COVID-19 and seasonal flu have some of the same symptoms. These include:

• Fever.
• Dry cough.
• Shortness of breath or trouble breathing.
• Feeling tired.
• Sore throat.
• Runny or stuffy nose.
• Muscle aches.
• Headache.

Feeling sick to your stomach or throwing up also can happen, but this is more common in children than in adults.

Some people who get COVID-19 or seasonal flu may have no symptoms. Some people may have mild symptoms. Others may get very sick.

You may need to get a test that shows which virus you have. You also can have both viruses at the same time.

Seasonal flu symptoms usually show up quickly, about 1 to 4 days after you're around someone who is sick. COVID-19 symptoms generally appear 2 to 14 days later. With COVID-19, you may have a new loss of taste or smell. That is rare with the flu.

Many people with seasonal flu or COVID-19 get better at home with rest and fluids. But some people become seriously ill and need to seek care in a hospital. Both COVID-19 and the flu can be deadly.

COVID-19 and the flu also can lead to serious health problems called complications. Some health problems that can happen because of getting COVID-19 or the flu include:

• Worsening of long-term conditions, such as heart disease.
• Pneumonia.
• Acute respiratory distress syndrome.
• Organ failure or problems.
• Heart or brain inflammation.
• Pregnancy complications.

COVID-19 and seasonal flu also can cause different complications. COVID-19 examples are blood clots, post-COVID conditions and multisystem inflammatory syndrome in children. Flu can lead to an infection by bacteria more often than COVID-19 infections do.

Medicines may be used to treat seasonal flu or COVID-19 if you are very sick or likely to get very sick. They also may be used if you are likely to have serious complications.

Your healthcare professional may give you an antiviral medicine to treat the flu. These medicines can include oseltamivir (Tamiflu), baloxavir (Xofluza) and zanamivir (Relenza).

If you are at high risk of getting very sick with COVID-19, your healthcare professional may give you medicine to keep you from getting worse. These medicines can include nirmatrelvir-ritonavir (Paxlovid), remdesivir (Veklury) or molnupiravir (Lagevrio).

But many people with seasonal flu or COVID-19 get better with rest, plenty of fluids and care that manages symptoms.

To lower the risk of serious influenza or COVID-19 illness, get the COVID-19 vaccine and seasonal flu vaccine. You can get both vaccines at the same visit if they are due at the same time.

Each year's flu vaccine protects from the flu viruses that are expected to be common that year. The vaccine can be given as a shot, also called an injection, or as a nasal spray.

The COVID-19 vaccines protect against the COVID-19 virus type expected to be the most common during the year.

You also can take steps to lower your risk of infection in other ways. These include:

• Stay away from people who are sick or have symptoms.
• Keep space between you and others when you are inside.
• Stay away from crowds and places with poor airflow.
• Wash your hands often with soap and water for at least 20 seconds. If you don't have soap, use an alcohol-based hand sanitizer with at least 60% alcohol.
• Wear a mask when you're inside a crowded place with poor airflow. This is most important when many people in the area are sick with COVID-19 or flu.
• Cover your mouth and nose with your elbow or a tissue when you cough or sneeze.
• Try not to touch your eyes, nose and mouth.
• Every day try to clean and disinfect things that people touch often, such as doorknobs, light switches and electronics.

These steps work best when you do them together.

If you have any questions about how likely you are to get very sick from COVID-19 or seasonal flu, talk with a healthcare professional.

How COVID-19 and flu spread

The viruses that cause COVID-19 and the flu spread in similar ways. They both can spread between people who are in close contact. They can spread farther when people are in a poorly ventilated indoor space. The viruses spread through respiratory droplets or aerosols released through talking, sneezing or coughing. These droplets can land in the mouth or nose of someone nearby or be inhaled. These viruses also can spread if a person touches a surface with one of the viruses on it and then touches the mouth, nose or eyes.

COVID-19 and flu symptoms

COVID-19 and the flu have many symptoms in common, including:

• Fever
• Cough
• Shortness of breath or difficulty breathing
• Tiredness
• Sore throat
• Runny or stuffy nose
• Muscle aches
• Headache
• Nausea or vomiting, but this is more common in children than in adults

The signs and symptoms of both diseases can range from no symptoms to mild or severe symptoms. Because COVID-19 and the flu have similar symptoms, it can be hard to diagnose which condition you have based on your symptoms alone. Testing may be done to see if you have COVID-19 or the flu. You also can have both diseases at the same time.

COVID-19 and flu complications

Both COVID-19 and the flu can lead to serious complications, such as:

• Pneumonia
• Acute respiratory distress syndrome
• Organ failure
• Heart attacks
• Heart or brain inflammation
• Stroke

Many people with the flu or mild symptoms of COVID-19 can recover at home with rest and fluids. But some people become seriously ill from the flu or COVID-19 and need to stay in the hospital. These infections also may be deadly.

COVID-19 and the flu have several differences, including different causes, complications and treatments. COVID-19 and the flu also spread differently, have different severity levels and a few different symptoms, and can be prevented by different vaccines.

COVID-19 and flu causes

COVID-19 and the flu are caused by different viruses. COVID-19 is caused by a coronavirus called SARS-CoV-2, while flu is caused by influenza A and B viruses.

COVID-19 and flu symptoms

Symptoms of COVID-19 and the flu appear at different times and have some differences. COVID-19 symptoms generally appear 2 to 14 days after exposure. Flu symptoms usually appear about 1 to 4 days after exposure.

COVID-19 and flu spread and severity

COVID-19 appears to be contagious for a longer time and to spread more quickly than the flu. With COVID-19, you may be more likely to experience loss of taste or smell.

Severe illness is more frequent with COVID-19 than with the flu. Compared with historical flu cases, COVID-19 may cause more hospital stays and death for people age 18 and older, even those who have no other health challenges.

So far, more than 95 million people have had COVID-19 in the U.S. as reported by the Centers for Disease Control and Prevention (CDC). More than 1 million people have died of COVID-19 in the U.S.

By comparison, during the 2021-2022 flu season in the U.S., between 8 and 13 million people had the flu and between 5,000 and 14,000 people died of the flu.

COVID-19 and flu complications

COVID-19 can cause different complications from the flu, such as blood clots, post-COVID conditions and multisystem inflammatory syndrome in children. Flu infection leads to secondary bacterial infection more often than COVID-19 infection does.

COVID-19 and flu treatments

Another difference is that the flu can be treated with a few different antiviral drugs. Two antiviral drugs, called remdesivir and Paxlovid, are currently approved to treat COVID-19. Researchers are evaluating many drugs and treatments for COVID-19. Some drugs may help reduce the severity of COVID-19.

COVID-19 and flu prevention

You can get an annual flu vaccine to help reduce your risk of the flu. The flu vaccine also can reduce the severity of the flu and the risk of serious complications.

Each year's flu vaccine provides protection from the three or four influenza viruses that are expected to be the most common during that year's flu season. The vaccine can be given as a shot, also called an injection, or as a nasal spray.

The flu vaccine doesn't prevent you from getting COVID-19. Also, research shows that getting the flu vaccine does not make you more likely to get other respiratory infections. Getting the flu vaccine may lower your risk of COVID-19 infection.

The U.S. Food and Drug Administration (FDA) has given emergency use authorization or approval to COVID-19 vaccines in the U.S. A vaccine can prevent you from getting the COVID-19 virus or prevent you from becoming seriously ill if you get the COVID-19 virus.

You are considered up to date with your vaccines if you have gotten all recommended COVID-19 vaccines when you become eligible.

Flu season in North America is highest in December, January and February. It's possible that the viruses that cause COVID-19 and the flu may spread in your community at the same time during the flu season. If this happens, people could become ill with one or both diseases at the same time.

Testing can determine which virus you may have and help guide health care providers to the appropriate treatment. People who become seriously ill from either virus may need to stay in the hospital, which could cause the hospitals to become full. Getting vaccinated for COVID-19 and the flu can help reduce the spread of the viruses that cause these diseases.

Get the COVID-19 vaccine and flu vaccine. You can get both at the same visit if they are due at the same time. You also can take the same steps to reduce your risk of infection from the viruses that cause COVID-19, the flu and other respiratory infections by following several standard precautions. The CDC recommends following these precautions:

• Avoid close contact with anyone who is sick or has symptoms.
• Keep distance between yourself and others when you're in indoor public spaces.
• Avoid crowds and indoor places that have poor airflow.
• Wash your hands often with soap and water for at least 20 seconds, or use an alcohol-based hand sanitizer that contains at least 60% alcohol.
• Wear a face mask in indoor public spaces if you're in an area with a high number of people with COVID-19 in the hospital. The CDC recommends wearing the most protective mask possible that you'll wear regularly, fits well and is comfortable.
• Cover your mouth and nose with your elbow or a tissue when you cough or sneeze.
• Avoid touching your eyes, nose and mouth.
• Clean and disinfect high-touch surfaces, such as doorknobs, light switches, electronics and counters, daily.

If you become sick with the flu, you can help prevent the spread of the flu by staying home and away from others. Continue to stay home until your fever has been gone for at least 24 hours.