The Flu vs COVID: A Comparison

Influenza (the flu) and COVID-19 are both contagious illnesses that infect the respiratory tract. While infection is caused by two distinct viruses (influenza viruses spread the flu and SARS-CoV-2 spreads COVID-19), symptoms of the flu and COVID-19 are similar so it is often hard to tell the difference between the two illnesses based on symptoms alone. Testing is likely necessary to confirm a diagnosis, and if you have any flu-like symptoms, you should get tested. Here, we will highlight a few key similarities between COVID-19 and the flu, and a few key differences.


Both influenza and COVID-19 are caused by viruses that infect your respiratory tract, so your immune system responds to infection in a very similar manner. This means that symptoms of both infections are very similar. Common symptoms between COVID-19 and the flu include:

  • Fever
  • Chills
  • Cough
  • Shortness of breath
  • Fatigue
  • Sore throat
  • Runny or stuffy nose
  • Body aches
  • Headache
  • In some, vomiting and diarrhea

COVID-19 and the flu are both spread via respiratory droplets, so prevention is very similar. Avoiding large events, maintaining 6 feet of distance, washing your hands, disinfecting surfaces, and wearing a mask are all standard precautions that reduce the risk of COVID-19 and the flu. (Research has found that following these measures may have helped shorten the length of the 2019-2020 flu season and lessened the number of people affected)


As mentioned previously, it is unlikely that you will be able to distinguish between COVID-19 and the flu based on symptoms alone. However, there are a few symptoms that are more likely to present in one illness as opposed to the other. Unlike the flu, COVID-19 can sometimes cause an infected person to lose their sense of taste or smell. Oftentimes, individuals with COVID-19 do not have any symptoms at all.

Because they are caused by different viruses, COVID-19 and the flu do have some key differences in infection. One key difference between COVID-19 and the flu is that the virus causing COVID-19 spreads more easily than influenza viruses. Additionally, a person infected with SARS-CoV-2 typically develops symptoms 5 days after being infected but symptoms can appear anywhere from 2 to 14 days after infection; for flu, the window is typically 1 to 4 days. This means that individuals infected with SARS-CoV2 are often contagious for longer before they are aware that they are sick.

While both illnesses can be mild or severe, COVID-19 causes more serious illness in certain groups of people, such as the elderly or immunocompromised. COVID-19 has a higher mortality rate and, in serious cases, can cause complications such as blood clots and multisystem inflammatory syndrome in children.

Another major difference between the flu and COVID-19 is our tools for treatment and prevention. Because we’ve studied influenza viruses extensively in comparison to the novel coronavirus, we have an annual flu vaccine and many FDA approved antiviral drugs that help to fight against influenza viruses in your body. These antiviral drugs have been shown to cause milder illness and reduce risk of death in individuals infected with influenza. The FDA has recently approved the antiviral drug remdesivir to be used against COVID-19, which can reduce recovery time in infected individuals but has not been shown to reduce mortality rate.

We also have an annual flu vaccine that, while not 100% effective, can reduce your risk of infection as well as the severity and risk of complications upon infection. We do not have a vaccine for COVID-19 (read about vaccine development here). The flu is caused by several different types and strains of influenza viruses, while COVID-19 is caused by the coronavirus known as SARS-CoV-2. Because of this, the flu vaccine has to be developed annually based on predictions as to which three to four influenza viruses are expected to be the most common that year.