COVID-19 vs. flu: Similarities and differences

During the COVID-19 pandemic, you may have heard that coronavirus disease 2019 (COVID-19) is similar to the flu (influenza). COVID-19 and the flu are both contagious respiratory diseases. They are both caused by viruses. They have some common symptoms. But COVID-19 and flu infections can affect people differently. Also, since the flu has been around much longer, health care providers know more about how to treat it, while they continue to learn more about COVID-19.

How are COVID-19 and the flu similar?

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.

What's the difference between COVID-19 and the flu?

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.

How might COVID-19 affect this year's flu season?

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.

How can I avoid getting COVID-19 and the flu?

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.