SARS-CoV-2 is a new coronavirus that emerged in late 2019. It causes a respiratory illness called COVID-19. Many people who get COVID-19 have a mild illness while others can become severely ill.

COVID-19 shares many similarities with seasonal influenza. However, there are also several differences between the two. Below, we’ll take a deeper dive into what we know so far about how COVID-19 differs from the flu.

COVID-19 and the flu both cause respiratory illness and the symptoms can be very similar. However, there are also key differences. Let’s break this down further.

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How Does COVID-19 Differ from the Flu?

The incubation period is the time that passes between the initial infection and the onset of symptoms.

  • COVID-19. The incubation period ranges between 2 and 14 days. According to the Centers for Disease Control and Prevention (CDC), the average incubation period is estimated to be 4 days.
  • Flu. The incubation period for the flu is shorter, averaging about 2 days and ranging between 1 and 4 days.

Let’s examine the symptoms of COVID-19 and the flu a little more closely.

COVID-19

The most commonly observed symptoms of COVID-19 are:

In addition to the symptoms above, some people may experience other symptoms, although these tend to be less common:

Some people with COVID-19 won’t experience any symptoms or may only experience very mild symptoms.

The flu

Individuals that have the flu experience some or all of the following symptoms:

  • fever
  • chills
  • cough
  • fatigue
  • body aches and pains
  • headache
  • runny or stuffy nose
  • sore throat
  • nausea or diarrhea

Not everyone with the flu will have a fever. This is particularly true in older adults or those who have a weakened immune system.

Additionally, digestive symptoms like vomiting and diarrhea are more common in children with the flu.

There are also some differences between COVID-19 and the flu in how symptoms present.

  • COVID-19. Initial symptoms of COVID-19 typically are milder, developing gradually.
  • Flu. The onset of flu symptoms is often sudden.

We’re learning more and more about COVID-19 every day and there are still aspects of this disease that aren’t fully known.

However, we do know that there are certain differences in the disease course and symptom severity of COVID-19 and the flu.

  • COVID-19. An estimated 20 percent of confirmed cases of COVID-19 are severe or critical. Some people may experience worsening of respiratory symptoms in the second week of illness, on average after 8 days.
  • Flu. An uncomplicated case of the flu typically resolves in about 3 to 7 days. In some people, cough and fatigue may linger for 2 weeks or longer. Just over 1 percent of people with the flu are hospitalized.

The period of time that a person with COVID-19 is contagious is still poorly understood. It’s currently believed that people are most contagious when they have symptoms.

It may also be possible to spread COVID-19 before you show symptoms. However, this isn’t currently believed to be a major factor in the illness’s spread. This could change, though, as we learn more about COVID-19.

A person with the flu can spread the virus beginning 1 day before they show symptoms. They can continue to spread the virus for a further 5 to 7 days after they become ill.

You may be wondering why COVID-19 is being treated differently than the flu and other respiratory viruses. Let’s explore this a little more.

Lack of immunity

COVID-19 is caused by a new type of coronavirus called SARS-CoV-2. Prior to its identification in late 2019, both the virus and the disease it causes were unknown. The exact source of the new coronavirus is unknown, though it’s believed to have an animal origin.

Unlike seasonal flu, the population as a whole doesn’t have much, if any, preexisting immunity to SARS-CoV-2. That means that it’s completely new to your immune system, which will have to work harder to generate a response to fight the virus.

Additionally, it’s currently unclear if people who’ve had COVID-19 can get it again. Future research will help to determine this.

Severity and mortality

COVID-19 is generally more severe than the flu. Data to date suggests that about 20 percent of people with COVID-19 experience severe or critical illness, requiring hospitalization and often the administration of oxygen or mechanical ventilation.

Although there are millions of flu cases each year in the United States, a smaller percentage of flu cases are estimated to result in hospitalization.

The results of studies on the exact mortality rate for COVID-19 have so far been varied. This calculation has been dependent on factors like location and population age.

Ranges from 0.25 to 3 percent have been estimated. One study of COVID-19 in Italy, in which almost a quarter of the population is 65 or older, puts the overall rate at 7.2 percent.

Nevertheless, these estimated mortality rates are higher than that of seasonal influenza, which is estimated to be about 0.1 percent.

Rate of transmission

Although studies are currently ongoing, it appears that the reproductive number (R0) for COVID-19 is higher than that of the flu.

R0 is the number of secondary infections that can be generated from a single infected individual. For COVID-19, R0 has been estimated to be 2.2. Estimates put the R0 of seasonal flu at about 1.28.

This information means that a person with COVID-19 can potentially transmit the infection to more people than the number of people someone with the flu can affect.

Treatments and vaccines

A vaccine is available for seasonal flu. It’s updated every year to target the influenza virus strains predicted to be the most common during flu season.

Getting a seasonal flu vaccine is the most effective way to prevent becoming sick with the flu. Although you can still get the flu after being vaccinated, your illness may be milder.

There are also antiviral medications available for the flu. If given early, they may help to lessen symptoms and shorten the amount of time that you’re sick.

There are currently no licensed vaccines available to protect against COVID-19. Additionally, there are no specific medications recommended for treatment of COVID-19. Researchers are hard at work on developing these.

COVID-19 and the flu are caused by viruses from completely different families. There’s currently no evidence that receiving the flu shot protects against COVID-19.

However, it’s still important to receive your flu shot each year to help protect yourself against the flu, particularly in at-risk groups. Remember that many of the same groups that are at risk for severe illness from COVID-19 are also at risk for severe illness from flu.

The flu follows a seasonal pattern, with cases being more prevalent in the cooler, drier months of the year. It’s currently unknown if COVID-19 will follow a similar pattern.

COVID-19 and flu are both transmitted via respiratory droplets that someone with the virus produces when they exhale, cough, or sneeze. If you inhale or come into contact with these droplets, you can contract the virus.

Additionally, respiratory droplets containing either the flu or new coronavirus can land on objects or surfaces. Touching a contaminated object or surface and then touching your face, mouth, or eyes may also lead to an infection.

A recent study of SARS-CoV-2, the novel coronavirus, found that viable virus could be found after:

  • up to 3 days on plastic and stainless steel
  • up to 24 hours on cardboard
  • up to 4 hours on copper

An older study on the flu found that viable virus could be detected on plastic and stainless steel for 24 to 48 hours. The virus was less stable on surfaces such as paper, cloth, and tissue, remaining viable between 8 and 12 hours.

There’s significant overlap between the at-risk groups for both illnesses. Factors that increase the risk of serious illness for both COVID-19 and the flu include:

Additionally, pregnant women and children under 2 years old are also at an increased risk of serious illness from the flu.

So what should you do if you have symptoms of COVID-19? Follow the steps below:

  • Isolate. Plan to stay at home and limit your contact with others except to receive medical care.
  • Check your symptoms. People with mild illness can often recover at home. However, keep an eye on your symptoms since they may worsen later in the infection.
  • Call your doctor. It’s always a good idea to call your doctor to let them know about the symptoms you’re experiencing.
  • Wear a face mask. If you’re living with others or going out to seek medical care, wear a surgical mask (if available). Also, call ahead before arriving at your doctor’s office.
  • Get tested. Currently, testing is limited. Your doctor can work with public health authorities to determine if you need to be tested for COVID-19.
  • Seek emergency care, if necessary. If you experience trouble breathing, chest pain, or blue face or lips, seek immediate medical attention.

COVID-19 and the flu are both respiratory illnesses. While there’s a lot of overlap between them, there are also key differences to look out for.

Many common symptoms of the flu aren’t common in cases of COVID-19. Flu symptoms also develop suddenly while COVID-19 symptoms develop gradually. Additionally, the incubation period for the flu is shorter.

COVID-19 also appears to cause more severe illness compared to the flu, with a larger percentage of people requiring hospitalization. The virus that causes COVID-19, SARS-CoV-2, also seems to transmit more readily in the population.

If you think that you have COVID-19, isolate yourself at home away from other people. Let your doctor know so that they can work to arrange testing. Be sure to keep careful track of your symptoms and seek prompt medical care if they begin to worsen.