First off, COVID-19 and the flu are both contagious respiratory illnesses, meaning they can be spread from an infected person or a noninfected person and affect a person's lungs and respiratory system.

While both are contagious respiratory illnesses, the flu and the coronavirus are caused by different viruses. Infection with a new coronavirus called SARS-CoV-2 causes COVID-19. Year-round, different types and subtypes of influenza viruses circulate. The flu is caused by infection with any type of influenza virus.

Flu and COVID-19 symptoms are incredibly similar. Both illnesses may cause fever or a feverish feeling, shortness of breath, difficulty breathing, cough, sore throat, runny or stuffy nose, fatigue, tiredness, muscle pain or body aches and headaches. Vomiting and diarrhea are also common symptoms in children but not adults. COVID-19 and flu patients both exhibit these symptoms to varying degrees, from no symptoms to severe ones.

Change or loss of taste or smell are two symptoms that set COVID-19 apart from the flu. However, given the many similar symptoms, it is difficult to tell the difference between the two based on symptoms alone. Anyone considering testing to determine which virus they have can look to the Centers for Disease Control and Prevention coronavirus self-checker for advice based on symptoms.

Although resulting in similar sorts of symptoms, COVID-19 does seem to cause more serious illnesses in some people than the flu. Accordingly, anyone experiencing severe COVID-19 symptoms like trouble breathing, confusion, bluish facial features, an inability to wake or stay awake or persistent pain or pressure in the chest should seek emergency medical care immediately.

It could take a day or more following infection for a person to begin experiencing symptoms of either the flu or COVID-19. Usually, a person infected with the flu develops symptoms one to four days after infection. A person infected with COVID-19 typically develops symptoms five days after infection.

While five days is typical, a person infected with COVID-19 may begin developing symptoms anywhere between two and 14 days after infection. Anyone who believes they may have contracted COVID-19 should contact a health care provider, start tracking symptoms and wear a mask around other people and pets, even at home.

Even if they are not exhibiting signs or symptoms, a person with the flu or COVID-19 can still be contagious. In most cases, people with the flu are contagious for about a day before showing symptoms. People with COVID-19 are contagious for about two days before showing symptoms.

Adults and older children who contract the flu are often contagious for the first day without symptoms, for three or four days of the illness and up to a week after. It’s possible for people with COVID-19 to spread the virus the two days before symptoms show and at least 10 days after. However, researchers are still working to understand how long a person with COVID-19 is contagious.

Just like COVID-19, the flu is spread by close contact between two people. Air droplets released when an infected person sneezes, coughs or talks land on nearby people who potentially inhale them.

Unlike the flu, COVID-19 has been known to have more superspreader events, instances when a single person in attendance infects many more. This results in continuous virus spread over time and points to COVID-19’s easy transferability.

It is possible for people to contract both illnesses via physical human contact like shaking hands or giving high-fives. Less commonly, a person can also get the flu or coronavirus by touching their face after touching a surface or object with the virus on it.

The flu and COVID-19 share several common severe complications, including pneumonia, heart attacks and strokes, respiratory failures, inflammation, bacterial infections, sepsis and fluid in lungs and more.

COVID-19 may cause other severe complications in adults too. After a coronavirus diagnosis, people may develop blood clots in the veins and arteries of the lungs, legs, heart or brain.

Older adults, pregnant people and people with existing health conditions are all at higher risk for severe illness after contracting either COVID-19 or the flu. To avoid contracting the coronavirus, those in these at-risk categories should limit contact with other people as much as possible and take precautions to reduce virus spread.

Any child under 5 years old, no matter how healthy, is at high risk for serious flu complications. Those under 2 years old are at even higher risk. Common severe complications caused by the flu include pneumonia, dehydration and long-term health problems like asthma and heart disease.

When infected with COVID-19, school-aged children are at a higher risk of multisystem inflammatory syndrome. Also called MIS-C, this severe condition results in varying body parts becoming inflamed, including the lungs, kidneys, heart and brain. Much is still to be learned about MIS-C, but the condition of most children who have been diagnosed with MIS-C has improved with medical care.

Antibiotics only work for certain bacterial infections. Accordingly, both the flu and COVID-19, two viral infections, cannot be treated with antibiotics. Instead, both COVID-19 and the flu are treated by addressing key symptoms.

Although not treatable by antibiotics, both the duration of the flu and COVID-19 can be shortened with some help from antiviral medications. These sorts of drugs are not sold over the counter and require a prescription from a healthcare provider. However, for mildly sick people, staying hydrated and over-the-counter drugs like acetaminophen (Tylenol) for COVID-19 and ibuprofen for the flu are helpful.

At this time, there is no vaccine available for COVID-19. However, several vaccines are in the process of being developed and approved. On the other hand, flu shots are available and preventive. Here is all you need to know about getting yours. 

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