COVID-19 and the Flu: What Is the Difference?

With Amesh Adalja MD

How to distinguish between the symptoms of the viruses this cold and flu season

COVID-19 and the flu

Autumn brings the beginning of many pleasant things: the leaves changing color, pumpkin pie, Halloween, and apple picking. Unfortunately, it also signals the advent of cold and flu season. Now, besides the usual threat of the flu this time of year, we have the threat of COVID-19 as well. 

How is COVID-19 different from the common cold or flu?

Medically, it can be surprisingly difficult to tell them apart without a confirmed test. Amesh Adalja MD, Senior Scholar for John Hopkins Center for Health Security, has been treating COVID-19 patients since the start of the epidemic as well as trying to educate the general public.  When asked how to distinguish between COVID-19 and the flu, he responded, “It's impossible to distinguish these clinically.” He went on to explain, "There’s no way to tell whether your symptoms are due to the common cold, or to COVID-19, or to influenza. That's why it's so important to get vaccinated for the flu now." 

Is COVID-19 really more deadly than the flu?

While initial symptoms of COVID-19 are in many ways identical to influenza, the risks are not.

Differences between the Coronavirus and influenza include:

  • COVID-19 has already killed over 219,000 people in the US, making it far more deadly than the common flu.
  • For seasonal influenza, the mortality rate is usually below .1%.
  • For COVID-19, the mortality rate can be as high as 3-4%.
  • According to the Centers for Disease Control and Prevention (CDC), COVID-19 also appears to be spread more easily than the flu because it is airborne. Patients take longer to develop symptoms and can remain contagious with COVID-19 for longer than influenza as well. 
  • Among COVID-19 patients, 80% of cases are asymptomatic or mild, while another 15% are serious infections needing oxygen and hospitalization, and 5% are critical infections requiring ventilation. This is a substantially larger rate of hospitalization and severe infections than the common flu. There are already indicators that COVID-19 may have long-term effects for patients, including pulmonary disease and cognitive impairment.   
  • While there is a yearly vaccine against influenza, there is as of yet no vaccine against COVID-19. 
  • Another key difference is the speed of transmission. Influenza has a shorter incubation period between the time of infection to the appearance of symptoms than COVID-19. 
  • Then there’s the serial interval. The serial interval is the time between successive cases of a virus. For influenza, the serial interval is about 72 hours. For COVID-19, it's about 5-6 days. This is another reason COVID-19 spreads faster than the flu.

What are the similarities between COVID-19 and the flu?

Common symptoms of the Coronavirus and influenza include:

  • Fever
  • Chills
  • Cough
  • Shortness of breath
  • Fatigue
  • Sore throat
  • Nasal congestion
  • Muscle aches
  • Headaches
  • Stomach issues including vomiting and diarrhea

Symptoms that are exclusive to COVID-19 (and not to the flu) include: 

  • A loss of sense of smell and taste
  • Conjunctivitis, aka pink or inflamed eyes
  • Blood clots in the veins and arteries of the lungs, heart, legs, or brain
  • Low blood-oxygen levels
  • Inability to breathe
  • Rashes and other skin issues
  • Brain fog, confusion, and other cognitive issues
  • Persistent chest pain or pressure
  • Feeling unable to wake or stay awake
  • Bluish face or lips

Additionally, COVID-19 can cause Multisystem Inflammatory Syndrome in Children (MIS-C). This is a syndrome where different body parts can become inflamed, including the heart, lungs, brain, kidneys, skin, and gastrointestinal organs. 

The CDC advises parents to contact a medical provider right away if their child displays the following symptoms:

  • Fever
  • Abdominal pain
  • Vomiting
  • Diarrhea
  • Neck pain
  • Rash
  • Bloodshot eyes
  • Extreme fatigue

The CDC advises parents to seek immediate emergency care if their child displays any of the following symptoms:

  • Difficulty breathing
  • Persistent chest pain or pressure
  • Confusion and/or cognitive difficulties
  • Inability to wake or stay awake
  • Bluish lips or face
  • Severe abdominal pain

Anyone experiencing the symptoms for COVID-19 and/or the flu should get in contact with their primary care doctor. And don’t panic!  Even if you do have COVID-19 rather than the common flu, 80% of cases are asymptomatic or mild. 

COVID-19 and influeza prevention tips

While there is no vaccine or cure for COVID-19, now is the time to get a flu vaccine and follow health guidelines to prevent the transmission of either virus. The following guidelines are advised by the Mayo Clinic based on recommendations from the Centers for Disease Control (CDC) as well as the World Health Organization (WHO). Following instructions to prevent the Coronavirus also has the advantage of reducing your risk of influenza, so it’s win-win!

  • Avoid large events and mass gatherings.
  • Avoid close contact with anyone who is sick or has symptoms.
  • Stay home as much as possible and keep a social distance of at least six feet between yourself and others, especially if you have a higher risk of serious illness. Keep in mind that some people may have COVID-19 and spread it to others, even if they don't have symptoms or don't know they have COVID-19.
  • Wash your hands often with soap and water for at least 20 seconds or use an alcohol-based hand sanitizer that contains at least 60% alcohol.
  • Cover your face with a cloth face mask in public spaces, such as the grocery store, where it's difficult to avoid close contact with others, especially if you're in an area with ongoing community spread. 
  • Cover your mouth and nose with your elbow or a tissue when you cough or sneeze. Throw away the used tissue. Wash your hands right away.
  • Avoid touching your eyes, nose, and mouth.
  • Avoid sharing dishes, glasses, towels, bedding, and other household items if you're sick.
  • Clean and disinfect high-touch surfaces, such as doorknobs, light switches, electronics, and counters.
  • Stay home from work, school, and public areas if you're sick, unless you're going to get medical care.
  • Avoid public transportation, taxis, and ridesharing if you're sick.
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