A healthy living blog from Marshfield Clinic Health System

COVID-19 and influenza: You can help prevent the spread of both

Editor’s note: This article was updated on Sept. 27, 2021. COVID-19 information and recommendations are subject to change. For the most up-to-date information, visit the Centers for Disease Control and Prevention (CDC) website or view our most recent COVID-19 blog posts.

This year, we again head into an influenza (flu) season in the midst of the COVID-19 pandemic. COVID-19 and influenza are both contagious respiratory illnesses caused by different viruses that can lead to missed school and work, hospitalization, and sometimes, death.

Because some of the symptoms of influenza and COVID-19 are similar, it may be difficult to tell the difference. Your health care provider will help by testing to confirm a diagnosis.

woman with mask on to prevent the spread of COVID-19 and flu

You can help prevent the spread of both COVID-19 and influenza.

In this post, Marshfield Clinic Health System experts share their advice to help protect you and others from COVID-19 and influenza.

Symptoms cannot identify the virus

COVID-19 and influenza can cause a variety of symptoms. You can have mild cold symptoms to severe, life-threatening pneumonia. And, unfortunately with COVID-19 and influenza (more common with COVID-19), you may not experience any symptoms, but can still spread the infection to others.

Common symptoms of COVID-19 and influenza include:

  • Fever or chills
  • Cough
  • Shortness of breath or difficulty breathing
  • Fatigue (tiredness)
  • Sore throat
  • Runny or stuffy nose
  • Muscle pain or body aches
  • Headache

“If you experience any of these symptoms, you should contact your doctor to be tested,” said Dr. Edward Belongia, an infectious disease epidemiologist at Marshfield Clinic Research Institute. “Many people with COVID-19 have mild illness or no symptoms, but they can still spread the virus to others. A lab test is the only way to distinguish flu and COVID-19 from other common viral infections.” Dr. Belongia emphasized the importance of seeking medical care early if you have a high risk condition such as heart disease, lung disease or diabetes. These people and others with certain chronic diseases have a higher risk of complications from the flu or COVID-19.

Loss of taste or smell is one symptom of COVID-19 that does not typically occur with influenza. It is important to contact your health care provider if you develop these symptoms or have had contact with a person who has COVID-19.

Spreading COVID-19 and influenza

The time interval from exposure to illness (incubation period) is about four to five days on average for COVID-19, and slightly shorter for influenza. The risk of spreading COVID-19 is greatest one to two days before symptoms develop and during the first few days of illness. A person with COVID-19 should remain isolated until at least 10 days have passed since illness began and symptoms have resolved for at least 24 hours. For influenza, Belongia said, “CDC recommends staying home for at least 24 hours after fever has resolved.”

The COVID-19 virus spreads through the air, and it is more contagious than the flu. Indoor group settings with poor ventilation are highest risk for spreading the virus. Flu and COVID-19 viruses are present in droplets from sneezing or coughing. Talking and singing can spread the virus to others in the same room. This is why facemask use and social distancing are so important. While all masks are important, some masks like KN95 or N95 will provide more protection. Although most transmission occurs indoors, the virus can also spread in crowded outdoor settings.

Flu and COVID-19 viruses also can spread from surfaces that are contaminated, although most transmission of COVID-19 occurs through the air. You can reduce the risk from contaminated surfaces by frequent handwashing and use of hand sanitizer.

“The delta variant of COVID-19 is twice as contagious and may cause more severe illness,” Belongia said. “Vaccination of all eligible people is essential to get the pandemic under control, including people who were previously infected. Vaccination greatly reduces the risk of infection and hospitalization, and it reduces the spread of the virus to other people.”

Vaccination and masking are the keys to controlling these viruses in the coming months. You should get the flu and COVID-19 vaccines as soon as possible to protect yourself, your family and your community. Unvaccinated people should always wear a high quality mask in public indoor settings. CDC also recommends indoor masking for fully vaccinated people in areas of substantial or high transmission. This currently includes central Wisconsin. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to schools, regardless of vaccination status. In general, you do not need to wear a mask outdoors unless you are in a crowd of people.

Call your provider to be tested

Testing for COVID-19 and influenza uses nasal swabs – maybe even one swab for both viruses – but the tests are different.

Health System providers will determine if you need testing and which tests should be ordered based on your symptoms and if you had close contact with someone who has COVID-19.

If you have flu-like symptoms or know you have been exposed to someone with COVID-19, you should contact your provider right away. In addition, the Health System has a 24-hour Nurse Line available at 844-342-6276 that can provide screening information and schedule testing if needed, or you can use the online screening to determine your next steps and schedule a testing appointment.

It can take one to two days to receive COVID-19 results from the lab, and less time than that for influenza results. While you wait for results, you need to continue to protect yourself and others by using safety precautions – stay home, wash your hands and clean high-touched areas. Click here for a handout on steps to take while you wait for COVID-19 results.


Centers for Disease Control and Prevention (CDC)

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