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 and transmission to complications—set the two respiratory illnesses apart.

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.

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 more mild of which can cause the common cold (although for the most part, colds are more likely to be caused by rhinoviruses), and the more severe of which can cause MERS and SARS.

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)

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

• Fever
• Dry cough 
• Fatigue
• Shortness of breath

Some patients experience additional symptoms:

• Sore throat
• Runny or stuffy nose
• Body aches
• Diarrhea

Approximately 1 out of every 6 people with COVID-19 will become seriously ill.

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. 

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 

• Pneumonia
• Severe acute respiratory syndrome
• Kidney failure

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

While WHO reported the numbers above, it's difficult to estimate the global or national mortality rate of COVID-19, notes Anju Goel, MD, MPH, a Verywell Health Medical Review Board member. This is because many people will experience a mild infection and will not be tested for the virus, she explains.

It’s important to note the flu mortality rate in the U.S. is less than 0.1%—much lower than the global rate. Of the 35 million Americans who got the flu last year, about 34,000 died.

Comparatively, of the 304,826 Americans with reported cases of COVID-19, 7,616 have died as of April 5. This equals roughly 2.5%, which is, again, lower than the estimated COVID-19 global mortality rate. 

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. 

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.

Annual flu shots are recommended by the CDC for everyone over 6 months old. 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)

There are currently no preventative vaccines, antiviral medications, or other treatments for COVID-19. However, clinical trials are underway.

A recent European study published as a pre-proof in the International Journal of Infectious Diseases suggests existing drugs may be able to treat COVID-19. While more research is needed, the authors looked at 120 broad-spectrum antiviral agents, deeming 31 of them potential treatments. 

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