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COVID-19, flu or RSV? Know the difference

Respiratory season is here, which means we will be seeing cases of COVID-19, influenza (flu) and respiratory syncytial virus (RSV) 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.

Child with virus 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.

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.”

People most vulnerable to severe RSV infection include infants, children with lung diseases, people ages 75 and older, younger people with serious chronic disease or weakened immune system and people living in long-term care facilities.

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 are at high risk for complications or if you have severe symptoms such as a high fever or shortness of breath. 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.

Effective treatment is available for COVID-19 and flu, and an antiviral drug may be prescribed for people who are at risk for serious illness.

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.

RSV vaccines

RSV vaccines have been licensed for more than a year to provide needed protection against the dangerous virus. The Centers for Disease Control and Prevention (CDC) recommends immunizations for adults ages 75 and older and adults ages 60 to 74 at an increased risk of severe RSV.*

To protect infants from RSV infection, an RSV vaccine also is recommended for pregnant women between 32-36 weeks pregnant, from September through January.** Another product, nirsevimab, is available for infants less than 8 months old, and high-risk infants between 8-19 months old at an increased risk of severe RSV disease and entering their second RSV reason. Nirsevimab is a monoclonal antibody product that is considered a passive immunization.

Learn more about the CDC RSV immunization recommendations. 

COVID-19 vaccines

“COVID cases are still being seen across the United States, and vaccination should be a priority for adults and children,” said Dr. Belongia. “In past years, COVID cases increased during winter. We may see a similar increase this season.”

The most recent version of the COVID-19 vaccine, the 2024-2025 vaccine, is designed to prevent infection with the currently circulating strains. Even if you have been vaccinated against COVID-19 in the past, getting a booster now will increase your level of protection.

The CDC recommends the 2024-25 COVID-19 vaccine for everyone aged 6 months and older. It is especially important for everyone over age 65 and people of all ages who are at risk for serious COVID-19.

Influenza vaccine

The current influenza vaccine also is formulated to protect against this year’s strains. The flu vaccine will lower your risk of getting the flu, and more importantly, it lowers your risk of being hospitalized.

Nearly 200 children died from influenza last season. Most of these deaths could have been prevented by vaccination,” said Dr. Belongia. “Nearly 90% of these children were not vaccinated against the flu.”

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 2024

Learn more: Caring for RSV at home

*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 pregnant women, adults ages 60-74 and adults 75 and older who received an RSV vaccine last year, you are not eligible to receive a dose this year.

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

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