A healthy living blog from Marshfield Clinic Health System

COVID-19, flu or RSV? Know the difference

COVID-19, influenza (flu) and respiratory syncytial virus (RSV) cases are being seen across the United States.

They’re all highly-contagious respiratory infections caused by viruses. These infections typically affect the lungs, airways or throat. While they’re seen year-round, there’s often a significant increase during fall and winter when people tend to spend more time inside. This allows viruses to pass more easily between people. Dry, cold air allows viruses to survive longer and cause more illness.

The three can be difficult to tell apart because they share many symptoms. However, knowing the difference can help you best determine the course of treatment.

The viruses share similar symptoms

RSV symptoms typically mirror that of a common cold, including runny nose, fatigue, cough and sore throat. More serious infections can cause difficulty breathing or wheezing.

“RSV poses a serious threat to older adults, especially people who are frail and those with heart or lung disease,” said Dr. Edward Belongia, an infectious disease epidemiologist at Marshfield Clinic Research Institute. “It is well-known to cause breathing problems in infants, but we now know it also can cause serious illness in adults.”

Child with COVID-19 flu or RSV blowing his nose

The three can be difficult to tell apart because they share many symptoms. However, knowing the difference can help you best determine the course of treatment.

People most vulnerable to severe RSV infection include infants, children with lung diseases, people ages 65 and older and people with weakened immune systems.

Both COVID and flu viruses can cause symptoms similar to RSV. This includes fever, chills, headache, cough, muscle aches, fatigue, shortness of breath, runny nose and sore throat. Doctors often rely on laboratory testing to identify the specific virus, since treatment options are different.

Seek medical care early if you have a high-risk condition such as heart disease, lung disease or diabetes and if you have symptoms compatible with the flu or COVID. People with certain chronic diseases may have a higher risk of complications from the flu or COVID.

Get tested to determine if you have COVID or the flu

The best way to know for certain what virus is causing your symptoms is to get tested.

“Early testing is important if you might have COVID or the flu,” said Dr. Belongia. “Treatment is most effective when started soon after symptoms begin.”

Testing for COVID and the flu uses nasal swabs, but the tests are different.

You also can purchase an over-the-counter test kit and test yourself at home for COVID-19. If you have a known exposure to someone with COVID, the best time to test is five days later. Keep in mind that over-the-counter tests can give false-negative results, especially early in the course of illness.

If you have flu-like symptoms or know you have been exposed to COVID and need to be tested, contact your provider or the Health System 24-hour Nurse Line at 844-342-6276.

Health care providers can prescribe Paxlovid for some people with COVID, including those 12 years and older who are at a higher risk for severe illness.

For those battling flu, there are treatments available to reduce the length of flu symptoms. Treatment is especially important for those over 65 years of age or less than 2 years of age, pregnant persons and those with chronic medical conditions.

While there is no specific treatment for RSV, a test is available and can be ordered by your provider. This is important for people with more severe illness and the test result can be helpful to minimize the risk of spreading the virus to other people.

Vaccines are available for COVID, flu and RSV

Immunizations are available for all three of these conditions and are more effective in preventing serious complications from occurring than treating the infection after it is diagnosed.

RSV vaccines have been licensed in the past year to provide needed protection against the dangerous virus. The Centers for Disease Control and Prevention (CDC) recommends immunizations for certain adults age 60 and older based on shared clinical decision making. Patients are encouraged to talk to their provider about their risk for serious RSV infection and the benefit of vaccination.

To protect infants from RSV infection, an RSV vaccine also is recommended for pregnant women between 32-36 weeks from September through January. A third product, nirsevimab, is a monoclonal antibody for administration to newborns, infants less than 8 months old, and high-risk infants less than 19 months of age from October through March.* Talk to your provider about options for RSV prevention if you are pregnant or have an infant.**

Learn more about the CDC RSV immunization recommendations. 

“COVID is still causing serious illness in Wisconsin, and vaccination should be a priority for adults and children,” said Dr. Belongia. “Last year, COVID cases increased during winter, and we may see a similar increase this season.”

The most recent version of the COVID-19 vaccine, the 2023 vaccine, is designed to prevent infection with the currently circulating strains, so even if you have been vaccinated against COVID-19 in the past, getting a booster now will increase your level of protection.

One dose is recommended for all adults and children age five and older. Younger children need multiple doses of the COVID vaccine to be up to date, including at least one dose of the updated 2023 vaccine.

Learn more: What you need to know about COVID-19 vaccine boosters.

The current influenza vaccine also is formulated to protect against this year’s strains. While not as effective as COVID-19 vaccine in preventing infection, it is very effective in preventing hospitalization and death due to influenza.

“More than 100 children died from influenza last season and most of these deaths could have been prevented by vaccination,” said Dr. Belongia.

Older adults are also at high risk for serious influenza illness. The flu vaccine is recommended for all adults and children who are at least six months of age.

Learn more: What’s new with the flu in 2023

Learn more: Caring for RSV at home

*Marshfield Clinic Health System and the nation are seeing shortages of the infant immunization (nirsevimab). The maternal vaccination may be the preferred option to protect infants against RSV.

**Coverage for the RSV immunizations may change depending on your insurance carrier. You are encouraged to call your insurance carrier prior to making an appointment to receive your vaccine.

For questions about COVID-19, influenza or RSV, talk to a Marshfield Clinic Health System provider.

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What’s new with the flu in 2023?

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