COVID-19 vs. the flu: How do I tell the difference?

Published September 24, 2020

Published

COVID-19 vs. the flu: How do I tell the difference?

With the flu season just around the corner and high numbers of COVID-19 cases still being diagnosed, you probably have questions. How do I tell the difference between the two, will my doctor know which illness I have and when do I seek medical attention?

While these viruses have many similarities, there are also some important differences. Several Nebraska Medicine physicians shed some light on these two viruses and how to best navigate them this fall.

How do COVID-19 and flu symptoms differ?

Both viruses cause respiratory disease, can affect different parts of the body, and can cause varying degrees of illness from mild or none to very severe symptoms, notes Alberto Marcelin, MD, family medicine physician. COVID-19 encompasses many, if not all of the symptoms that typically occur with the influenza virus including fever, fatigue, cough, shortness of breath and gastrointestinal problems. With COVID-19, many people also report a change or loss of taste or smell. 

How do you know whether you have the flu or COVID-19? 

Because symptoms can be so similar, it may be difficult for you and even your doctor to determine if you have the flu or COVID-19 until you have been tested, says Dr. Marcelin. If you suspect you have the flu or the coronavirus, it is best to contact your clinician by phone for evaluation and to arrange testing if appropriate. 

Is COVID-19 more severe than the flu? 

"When comparing the two, the seriousness of the influenza virus should not be downplayed," says David Brett-Major, MD, MH, infectious diseases specialist. "The seasonal flu is a terrible virus that causes lots of illness and deaths each year. Now we will have both at play this season."

When looking at total cases to date, in the 2019-2020 flu season, there were up to 56 million flu like illnesses diagnosed. Over the last six months, there have been more than 6.8 million people diagnosed with COVID-19. 

However, far more people have already died from COVID-19 than died from influenza last year, and the deaths from COVID-19 continue to rise daily. In the United States nearly 3% (more than 200,000 people) of everyone who has a diagnosis of COVID-19 has died, compared to .1% for seasonal influenza cases (up to 62,000) last year.

There may be several reasons for this. "Some of this may be due to undercounting of influenza cases and their indirect effect on people who have underlying disease," says Dr. Brett-Major. "It may also be related to the fact that SARS-CoV-2, the virus that causes COVID-19, is a new virus, so our bodies have less immune system experience with the virus in contrast to influenza. How the SARS-CoV-2 virus behaves in the body may also be a contributing factor."

How quickly will I develop symptoms of COVID-19 compared to the flu? 

According to the Centers for Disease Control and Prevention, COVID-19 has an incubation period of up to 14 days and the average time from infection to becoming symptomatic is five days. While the exact time from infection to the ability to transmit the disease is uncertain, it is believed that the virus can be transmitted to another person approximately two days before symptoms start.

In comparison, flu virus symptoms usually begin more quickly – in about two days. Like COVID-19, people with the flu can pass it on to someone else before they know they are sick.

How contagious is the flu compared to COVID-19?

Direct contact with respiratory droplets has been the primary known method of transmission for both diseases. These droplets usually do not travel more than 6 feet, which is why it is recommended that people stay 6 feet apart. Environmental conditions, however, can change that quite a bit, notes Dr. Brett-Major. For instance, if you are in close quarters without air exchanges, risk of transmission may be greater.

Additionally, a new study by UNMC researchers indicates that airborne particles with SARS-CoV-2 also can be detected in COVID-19 patient care areas. (SARS-CoV-2 is the virus that causes COVID-19.) While we know that COVID-19 can be spread by large respiratory droplets caused by coughing or sneezing, tiny respiratory droplets called aerosols may also spread COVID-19 under the right conditions. Aerosols are small enough to float further than large respiratory droplets, which are heavier and fall more quickly to the ground. 


"While the majority of people with both influenza or COVID have no symptoms or very mild symptoms, people with COVID-19 release the virus into the environment for more days than people with influenza so they can infect more people," notes Heather Strah, MD, pulmonary medicine and critical care specialist. Individuals infected with COVID-19 typically can spread the virus for about two days before symptoms begin and may continue to be contagious for 10 days or more after symptoms first appear, according to the CDC.

In addition, most people who develop the flu are contagious for about one day before symptoms appear. And because symptoms usually appear more quickly, they can isolate themselves from others early on, notes Dr. Strah. People with the flu are usually contagious for the initial three to four days while they are ill and for about seven days after. 

COVID-19 also appears to be more contagious among specific age groups and certain populations, says the CDC. 

What are the long-term effects on the organs for the flu and COVID-19?

Severe cases of both influenza and COVID-19 can have long term effects on the organs such as the lungs, heart and kidneys, says Dr. Marcelin.

How does treatment differ for these two viruses?

There are antiviral medications now for both moderate to severe COVID-19 and the flu. For people with mild to moderate symptoms who are receiving outpatient care, treatment involves managing the symptoms with lots of rest, fluids, and over the counter pain medications like acetaminophen and ibuprofen. 

Remdesivir is the antiviral drug approved for COVID-19 under emergency use authorization and is used for sicker patients. Low dose dexamethasone is also being used for patients needing supplemental oxygen. These drugs do not cure the disease, but help how quickly some people recover, notes Dr. Marcelin. Similarly, for influenza, a drug called oseltamivir, commonly known as Tamiflu®, treats the viral infection and reduces viral shed. It is most effective if given within two days of symptoms starting. 

When is it time to seek medical attention?

"Since COVID-19 can affect multiple organs in the body, it presents with different symptoms for different individuals," says Dr. Marcelin. "Call your doctor if you experience symptoms such as shortness of breath, sustained temperature of 100.4 or greater, loss of taste or smell. If you are unable to resume your usual activities after recovering from COVID-19, you should contact your physician as soon as possible to determine if further interventions are necessary." 

Likewise, for the flu, if you experience trouble breathing, chest pain, severe or persistent vomiting or flu symptoms that appear to get better and then return with a fever or worse cough, call your doctor. 

Will the flu vaccine provide any protection against COVID-19? 

The influenza immunization is effective against influenza only. "This year, more than ever, it will be very important to receive the flu vaccination," says Dr. Marcelin. "At this time, we do not know how effective our immune system will be at fighting the disease if someone becomes sick with both the flu and coronavirus simultaneously."

When the COVID-19 vaccine becomes available, are there any reasons why I should not receive it?

Barring any unforeseen developments, if a safe and effective vaccine is available, you should consider getting it, says Dr. Marcelin. We do not know enough about COVID-19 vaccines yet to know which people should get that vaccine and who should not.  

Will wearing masks reduce the spread of the flu as well as COVID-19?

Multiple studies have shown that wearing a face covering decreases transmission of respiratory droplets and the potential of infection. Since the flu is also spread by respiratory droplets, wearing masks should be beneficial in reducing the spread of flu also, says Dr. Brett-Major. Hand hygiene, social distancing and environmental hygiene also are important to decrease transmission of the virus.