Differences between Influenza (flu) and COVID-19

Early in the pandemic, there was some confusion as to whether people should worry about COVID-19 as it was being compared to the flu. We now know that while the flu and COVID-19 are both contagious respiratory illnesses, they are caused by two different viruses.  

COVID-19 is caused by infection from a new coronavirus (SARS-CoV-2) whereas the flu is caused by infection from the influenza viruses. Furthermore, according to the CDC, COVID-19 seems to spread more easily than the flu and causes more serious illnesses in some people. It can also take longer for people infected with COVID-19 to show symptoms and they can be contagious for longer.  

However, because the flu and COVID-19 share some symptoms, it may be difficult to tell the difference between the two based on symptoms alone. To confirm a diagnosis of COVID-19, it is recommended that you get tested. Additional similarities and differences between COVID-19 and the flu are discussed below: 

Similarities between COVID-19 and flu symptoms include: 

  • Fever or feeling feverish/chills 
  • Cough 
  • Shortness of breath or difficulty breathing  
  • Sore throat 
  • Runny or stuffy nose 
  • Muscle pain or body aches 
  • Headache  
  • Vomiting or diarrhea (these are more common in children than adults) 

 

Differences between COVID-19 and flu symptoms: 

  • Flu viruses can cause mild to severe illness, including sinus and ear infections as moderate complications from flu, while pneumonia is a serious flu complication. Other serious complications of the flu are inflammation of the heart, brain or muscle tissues and multi-organ failure.  
  • COVID-19 seems to cause more serious illnesses in some people, and other signs not seen with the flu may include a change in or loss of taste or smell. 

 

Length of symptoms following exposure and infection: 

  • Similarities: for both COVID-19 and flu: 1 or more days can pass between a person becoming infected and when he or she starts to experience illness symptoms 
  • Differences: if a person has COVID-19, it can take longer to develop symptoms than if they have the flu 

 

Typically, if a person has the flu, they can develop symptoms anywhere from 1 to 4 days after infection 

In the case of COVID-19, the norm is to develop symptoms 5 days after being infected, but symptoms can appear as early as 2 days after infection or as late as 14 days after infection. This is why it is recommended that if you know or think that you have been exposed to COVID-19, you should quarantine for 14 days and monitor yourself.  

Length of time that you’re contagious: 

  • Similarities: for both COVID-19 and flu, it is possible to spread the virus for at least 1 day before experiencing any symptoms  
  • Differences: if someone has covid-19, they may be contagious for a longer period than if they had the flu 

 

Most people with the flu are contagious for about 1 day before they show symptoms. Older children and adults with the flu can be contagious during the initial 3-4 days of their illness but many remain contagious for about 7 days. 

In the case of COVID-19, how long someone can spread the virus to others is still under investigation. It is possible for people to spread the virus for about 2 days before they show symptoms and remain contagious for at least 10 days after the first symptoms appeared. If someone is not showing symptoms or their symptoms go away, it is possible to remain contagious for at least 10 days after testing positive for the virus.  

How they spread: 

  • Similarities:  
    • Both COVID-19 and flu can spread from person to person, especially those that are less than 6 feet from one other.  
    • Both spread mainly by droplets made when people infected with them cough, sneeze or talk. These droplets can then land in the mouths, noses or be inhaled into the lungs of those nearby.  
    • Although less common, it is also possible to get infected by physical human contact (I.e., shaking hands) or by touching a surface or object that has the virus on it and then touching your own mouth, nose of eyes 
    • Both the flu virus and COVID-19 may spread to others before the infected person starts showing symptoms, by people with very mild symptoms or by people who are asymptomatic and never developed any symptoms 
  • Differences:  
    • Although both COVID-19 and the flu viruses are believed to spread in similar ways, COVID-19 has proven to be more contagious among certain populations and age groups than the flu.  
    • COVID-19 has also been observed to have more superspreading events than the flu. What this means is that the COVID-19 virus can quickly and easily spread to a lot of people and result in continuous spreading among people as time progresses. 

 

People at high-risk for COVID-19 and/or the flu: 

  • Similarities:
    • Both COVID-19 and the flu can result in severe illness and complications. For both illnesses, those at the highest risk include:  
      • Older adults 
      • People with certain underlying medical conditions 
      • Pregnant people  
  • Differences:  
    • The risk of complications for healthy children is higher for flu compared to COVID-19. However, infants and children with underlying medical conditions are at increased risk for both flu and COVID-19 
    • For the flu: young children are at higher risk of severe illness from flu 
    • For COVID-19: school-aged children infected with COVID-19 are at higher risk of Multisystem Inflammatory Syndrome in Children (MIS-C), a rare but severe complication of COVID-19. 

 

Complications of the flu and/or COVID-19: 

  • Similarities:
    • Both COVID-19 and the flu can result in the following complications:  
      • Pneumonia 
      • Respiratory failure 
      • Acute respiratory distress syndrome (fluid in the lungs) 
      • Sepsis 
      • Cardiac injury (I.e., heart attacks) 
      • Multiple-organ failure (respiratory failure, kidney failure, shock) 
      • Secondary bacterial infections (infections that occur in people who have previously been infected with COVID-19 or the flu) 
  • Differences:  
    • Flu: most people who get the flu will recover in a few days to less than two weeks while some others may develop complications. 
    • COVID-19: additional complications associated with COVID-19 are:  
    • Blood clots in the veins and arteries of the lungs, heart, legs or brain  
    • Multisystem inflammatory syndrome in children (MIS-C)  

 

Approved Treatments  

  • Similarities:
    • people at high-risk of complications or who have been hospitalized for either COVID-19 or the flu should receive medical care to help relieve symptoms and reduce the likelihood of complications 
  • Differences:  
    • Flu: the FDA has approved four antiviral drugs to treat those hospitalized with the flu. These treatments should be given as soon as possible.  
  • COVID-19: because this is a new virus in humans, possible treatments for COVID-19 are still being explored and regularly updated as new evidence emerges. Currently, only Remdesivir has been given an Emergency Use Authorization (EUA) as an exploratory treatment for COVID-19. 

Vaccines 

  • Similarities:
    • vaccines for both COVID-19 and the flu must be approved or authorized for emergency use (EUA) by the FDA before they can be given to the public  
  • Differences:  
    • Flu: there are multiple FDA-licensed flu vaccines produced annually to protect against the 3-4 flu viruses that scientists believe circulate each year. This is why it is recommended that you get your flu vaccine every year.  
    • COVID-19: Currently two vaccines have been approved for use by the FDA under an Emergency Use Authorization (EUA). These are the Pfizer and Moderna vaccines, which have been distributed to many frontline healthcare workers and is now being distributed to elderly Americans. Other vaccines are still under development like the Johnson & Johnson single dose vaccine which has recently applied for an EUA.