Coronavirus (COVID-19) and the Flu: Similarities and Differences

Part of what makes the novel coronavirus (COVID-19) so concerning is how innocuous initial symptoms can be. Just like the flu, COVID-19 most commonly begins with fever, tiredness, and coughing.

However, many factors—ranging from cause to complications—set the two respiratory illnesses apart.

Causes

Different viruses cause influenza and COVID-19.

Flu Causes

All types of flu—the most common of which is influenza A—are caused by an influenza virus. There are hundreds of strains that mutate often. For example, influenza A comes in two subtypes and many strains; H1N1 is the strain that caused swine flu in 2009. Beyond that, influenza B, C, and D also exist.

Coronavirus (COVID-19) Causes

COVID-19, on the other hand, is caused by a virus called SARS-CoV-2. It's part of a larger family of coronaviruses.

The milder coronaviruses can cause the common cold (although for the most part, colds are more likely to be caused by rhinoviruses). The more severe strains can cause Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS).

Symptoms

The two illnesses vary somewhat in symptoms, although there are still emerging details as to the symptoms and illness progression for COVID-19.

Flu Symptoms

Seasonal influenza comes on suddenly. Its incubation period—the period of time between contracting the virus and showing symptoms—is 1 to 4 days. It typically causes several symptoms:

• Fever or chills (not everyone with the flu will experience this)
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue
• Vomiting and diarrhea (more common in children than adults)

Coronavirus (COVID-19) Symptoms

COVID-19 symptoms may appear 1 to 14 days after initial exposure. The most commonly include:

• Fever
• Dry cough 
• Fatigue
• Shortness of breath

Some patients experience additional symptoms:

• Sore throat
• Runny or stuffy nose
• Body aches
• Diarrhea
• Loss of taste or smell

Approximately one out of every six people with COVID-19 will become seriously ill.

Complications

Clearly, the flu and COVID-19 have quite a bit of symptom overlap. But the complications of the illnesses are where they start diverge a little more. 

At a March 3 press briefing, WHO Director-General Dr. Tedros Adhanom Ghebreyesus said that globally, COVID-19 causes more severe disease than seasonal influenza. The reason? Many people around the world have built up immunity to seasonal flu strains.

But since COVID-19 is brand new, no one has immunity. As a result, infection is more likely, and some of those infections will result in severe illness. 

Flu Complications 

Moderate: 

• Sinus infection
• Ear infection 

Serious:

• Pneumonia
• Heart inflammation (myocarditis)
• Brain inflammation (encephalitis)
• Muscle tissue inflammation (rhabdomyolysis) 
• Multi-organ failure 
• Sepsis
• Worsening of chronic conditions 

Coronavirus (COVID-19) Complications

• Pneumonia
• Severe acute respiratory syndrome
• Kidney failure

The most serious complication of both the flu and COVID-19 is death. 

Transmission

Both the flu and COVID-19 can be spread by respiratory droplets from an infected person. But current WHO data suggests one person with COVID-19 infects between 2 and 2.5 people on average, compared to someone with the seasonal flu, who will infect an average of 1.3 people.

Still, WHO says flu spreads faster than COVID-19, since it has a shorter incubation period and a shorter time between successive cases. 

Treatment

A major difference between the flu and COVID-19 is that the former has both preventative and curative treatments, and the latter does not. The more mild symptoms of both conditions can be treated with over-the-counter pain medications, fever reducers, and cough medicines.

Flu Prevention and Treatment 

Annual flu shots are recommended by the CDC for everyone 6 months of age and older. While their effectiveness varies every year, recent studies show vaccines reduce flu risk by 40% to 60%. Even if you do get the flu after being vaccinated, the shot lessens the severity of symptoms and protects against complications. 

Antiviral medications are available with a prescription and can shorten the duration of flu symptoms if taken within 48 hours of symptom onset. They can also prevent the flu if you’ve been in close contact with someone who’s been diagnosed. 

The FDA has approved these antiviral medications for the flu:

• Tamiflu (oseltamivir phosphate)
• Relenza (zanamivir)
• Rapivab (peramivir)
• Xofluza (baloxavir marboxil)

Coronavirus (COVID-19) Prevention and Treatment

There are currently no preventative vaccines, antiviral medications, or other treatments for COVID-19. However, on May 1, the antiviral remdesivir—initially developed by Gilead Sciences for Ebola—became the first treatment option for COVID-19 to receive emergency use authorization from the FDA.

The FDA has permitted remdesivir to be used in adults and children hospitalized with severe cases of the disease. In addition, clinical trials for other treatments are underway, many of which are examining whether existing drugs can target COVID-19 safely.

While a lack of treatment sounds scary, about 80% of people recover from coronavirus without needing special treatment.