Coronavirus vs. flu: Similarities, differences

During the COVID-19 pandemic, you may have heard that COVID-19 is similar to the flu (influenza). Both are contagious respiratory diseases caused by viruses.

They have some common symptoms. But through closer comparison, they can affect people differently. Also, since the flu has been around much longer, doctors know more about how to treat and prevent it, while they continue to learn more about COVID-19.

How are COVID-19 and the flu similar?

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 (within 6 feet). 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 his or her mouth, nose or eyes.

COVID-19 and flu symptoms

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

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

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 can also 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
• Death

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.

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 new coronavirus called SARS-CoV-2, while influenza 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 two to 14 days after exposure. Flu symptoms usually appear about one to four days after exposure.

COVID-19 and flu spread and severity

COVID-19 appears to be more contagious and spread more quickly than the flu. With COVID-19, you may experience loss of taste or smell. Severe illness, such as lung injury, may be more frequent with COVID-19 than with influenza. The mortality rate is higher with COVID-19 than the flu.

So far, more than 39 million people have had COVID-19 in the U.S. as reported by the Centers for Disease Control and Prevention (CDC). More than 630,000 people have died from COVID-19 in the U.S. in 2020 and 2021. By comparison, during the 2019–2020 flu season in the U.S., about 38 million people had the flu and about 22,000 died of the flu.

COVID-19 and flu complications

COVID-19 can cause different complications from the flu, such as blood clots and multisystem inflammatory syndrome in children.

COVID-19 and flu treatments

Another difference is that the flu can be treated with antiviral drugs. Only one antiviral drug, called remdesivir, is 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 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 (injection) or nasal spray.

The flu vaccine doesn't prevent you from getting COVID-19. Some research has found getting a flu vaccine might lower the risk of getting COVID-19. Research also shows that getting the flu vaccine does not make you more likely to get COVID-19 or other respiratory infections.

The U.S. Food and Drug Administration (FDA) has given emergency use authorization to some COVID-19 vaccines in the U.S., and one vaccine has been approved. 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. Getting a COVID-19 vaccine will also allow you to start doing many things that you might not have been able to do because of the pandemic, including not wearing a mask or social distancing — except where required by a rule or law. No vaccine is currently available to the public for the virus that causes COVID-19. But researchers are working to develop vaccines to prevent COVID-19 and continue to make progress.

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

Flu season in North America typically occurs between October and May. 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 doctors to the appropriate treatment. People who become seriously ill from either disease may need to stay in the hospital at the same time, which could cause hospitals to become full. Getting vaccinated for COVID-19 or the flu can help reduce the spread of the viruses that cause these diseases.

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

Get the COVID-19 vaccine and flu vaccines when they're available to you. 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.

In fact, some research has found that following these measures, such as social distancing and wearing a face mask, may have helped shorten the length of the flu season and decreased the number of people affected in the 2019-2020 flu season.

If you haven't had the COVID-19 vaccine, you can take may steps to reduce your risk of infection.

Precautions may include:

• Avoiding large events and mass gatherings.
• Avoiding close contact (within 6 feet) with anyone outside your household, especially if you have a higher risk of serious illness.
• Washing your hands often with soap and water for at least 20 seconds or using an alcohol-based hand sanitizer that contains at least 60% alcohol.
• Wearing a cloth face mask when you're in indoor public spaces and outdoors where this is a high risk of COVID-19 transmission, such as at a crowded event or large gathering. Further COVID-19 mask guidance differs depending on whether you are fully vaccinated or unvaccinated.
• Covering your mouth and nose with your elbow or a tissue when you cough or sneeze.
• Avoiding touching your eyes, nose and mouth.
• Cleaning and disinfecting high-touch surfaces, such as doorknobs, light switches, electronics and counters daily.

Taking these prevention measures can help you stay healthy and reduce your risk of becoming ill with COVID-19 or the flu.

This article is written by Mayo Clinic staff and originally published on mayoclinic.org.