Though caused by different viruses, influenza (also called the flu) can be mistaken for coronavirus (COVID-19) because of their similar symptoms.
Understanding the differences between the two can help you determine whether or not you need to isolate, get tested, or seek care.
In this article, I’ll describe many of the similarities and differences between COVID-19 and the flu, including the symptoms, causes, diagnosis, treatment, severity, complications, and prevention of each.
I’ll also cover how the flu vaccine and COVID-19 vaccines differ.
Finally, I’ll explain when you should see a healthcare provider about your symptoms so you can receive an accurate diagnosis and proper treatment.
COVID-19 and Flu Basics
Because of their shared symptoms, ways of spreading, and complications, it can be very challenging for someone to know whether they may be infected with the flu or COVID-19.
However, it’s important to identify which virus may be causing your symptoms, as the flu and COVID-19 have vastly different risks and outcomes and require different kinds of care.
Both the flu and COVID-19 are highly infectious respiratory illnesses caused by viruses.
Both spread through airborne droplets and can result in serious complications, including pneumonia, organ failure, and death.
Older adults, the immunocompromised, and young children are at a higher risk of severe illness and complications from both COVID-19 and the flu. Both also have FDA-approved and FDA-authorized vaccines.
Compared with those who come down with the flu, people who contract COVID-19 have a higher risk of severe illness, hospitalization, and death.
COVID-19 also has a longer incubation period (the time between exposure and the first appearance of symptoms), and its symptoms tend to last longer than those caused by the flu.
Additionally, while both vaccines are effective, COVID-19 vaccines are more so.
The mRNA COVID-19 vaccines from Pfizer-BioN-Tech and Moderna are both more than 90% effective effective at preventing severe illness up to six months after the second shot.
One of the biggest difficulties in differentiating between a COVID-19 infection and the flu is their shared symptoms.
However, there are some ways in which their symptoms differ.
Some symptoms can appear with both COVID-19 and the flu:
However, some symptoms of COVID-19 are extremely rare with the flu:
And symptoms that are common with the flu but seen less often with COVID-19 include:
COVID-19 and the flu are both viral infections, but they’re caused by different viruses.
Both viruses are highly contagious and spread in people through respiratory droplets.
There are also multiple strains of both the flu and COVID-19.
COVID-19 is spread by the SARS-CoV-2 virus, a type of coronavirus that was discovered in 2019.
Influenza A and B viruses are responsible for most seasonal flu epidemics in the U.S each year.
If you’re experiencing symptoms and want to know if you have the flu or COVID-19, similar methods can help diagnose your illness.
Both COVID-19 and the flu can be diagnosed through a polymerase chain reaction (PCR) test.
In fact, many of these tests are used to diagnose both influenza and COVID-19.
Keep in mind that it’s possible to have both infections at the same time.
During flu season, your doctor may diagnose you with influenza based on your symptoms alone.
For COVID-19, a PCR or antigen test is required to officially diagnose the infection.
Mild cases of both COVID-19 and the flu can often be managed at home.
But if you have a severe infection of either, you may require hospitalization, where different types of treatment are available depending on your infection.
In mild infections of both COVID-19 and the flu, rest, plenty of fluids, and over-the-counter (OTC) medications are often all that’s needed to manage and soothe symptoms.
In more severe cases, people with the flu and COVID-19 should receive supportive medical care in the hospital.
Several prescription antiviral drugs are FDA-approved to treat the flu.
To date, only one antiviral drug, remdesivir (Veklury), is FDA-approved to treat COVID-19.
Due to the emergency state of the pandemic, the FDA has also issued emergency use authorizations (EUAs) to allow healthcare professionals to use other investigational products that have not yet been approved to treat COVID-19 patients.
Severity and Spread
COVID-19 and the flu are both highly infectious illnesses that spread easily between people.
However, evidence shows that COVID-19 is more contagious and can cause more serious illness in some people.
Both COVID-19 and the flu are largely spread through person-to-person contact via small airborne particles.
People infected with either virus can be contagious before showing symptoms, when experiencing mild symptoms, or when asymptomatic (without any symptoms).
COVID-19 is generally more contagious than the flu and is more likely to cause severe illness and death.
There have also been more “superspreader” events (gatherings where even just a single infected person causes many others to contract a virus) with COVID-19 than with the flu.
Complications and Risks
Both COVID-19 and the flu can cause severe illness, hospitalization, complications, and death.
However, the risks and rates of complications are higher with COVID-19 than with the flu.
COVID-19 and the flu can cause similar complications, including:
- Respiratory failure
- Acute respiratory distress syndrome
- Cardiac injury
- Multiple-organ failure
- Worsening of chronic medical conditions
- Inflammation of the heart, brain, or muscle tissues
- Secondary bacterial or fungal infections
COVID-19 causes more serious illness, hospitalization, and death than the flu.
Between 2019 and 2020 in the U.S., 22,000 people died of the flu and more than 630,000 people died of COVID-19.
Additionally, long-lasting symptoms that persist after the initial infection clears are more prevalent with COVID-19 than with the flu.
Similar practices can help prevent COVID-19 and the flu.
Everyday actions can help prevent infections from both viruses:
- Limiting person-to-person contact
- Wearing a mask in public
- Washing hands thoroughly and frequently
- Ventilating indoor spaces
- Getting vaccinated when eligible
There are no major differences in COVID-19 and flu prevention.
Both COVID-19 and the flu have FDA-approved and authorized vaccines.
Flu and COVID-19 vaccines are effective at preventing infection, severe illness, and death.
COVID-19 vaccines are more effective than flu vaccines.
Up to six months after receiving the second dose, the Pfizer-BioN-Tech and Moderna mRNA COVID-19 vaccines are more than 90% effective effective at preventing severe illness.
Meanwhile, flu vaccines reduce the risk of illness by 40-60% in the general population.
Another difference between the vaccines is that the flu vaccines change from year to year depending on which strains of the influenza virus are most prevalent that year.
When to See a Doctor
If you experience any severe symptoms of a COVID-19 or the flu, seek urgent care immediately:
- Trouble breathing
- Persistent chest pain and/or pressure
- New confusion
- Inability to wake or stay awake
- Pale, gray, or blue-colored skin
How K Health Can Help
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Download K Health to check your symptoms, explore conditions and treatments, and, if needed, text with a clinician in minutes. K Health’s AI-powered app is based on 20 years of clinical data.
Frequently Asked Questions
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
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Comparing the COVID-19 Vaccines: How Are They Different? (2021).
How COVID-19 Is Different and Worse than the Flu. (2020).
Influenza (Flu). (2021).
Is It COVID-19 or Is It the Flu? (2021).
Symptoms of COVID-19. (2021).
Vaccine Effectiveness: How Well Do Flu Vaccines Work? (2021).