COVID-19 vs. flu: Similarities and differences

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.

What causes COVID-19 and flu?

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.

How do COVID-19 and flu spread?

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 and flu spread and severity

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.

What symptoms do COVID-19 and flu have in common?

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.

Differences between COVID-19 and flu symptoms

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.

COVID-19 and flu complications

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.

What medicines are used to treat COVID-19 and flu?

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.

What can I do to keep from getting COVID-19 or flu?

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.