​How Do You Know if You Have COVID-19, Flu, or RSV?

Woman not feeling well in bed

Respiratory illnesses are on the rise again. But it can be hard to determine whether you have RSV, the flu, or COVID-19.

If you are feeling ill, you could be suffering from one of these illnesses.

But you can take precautions to protect yourself and others. Those include knowing symptoms, understanding how these illnesses spread, and staying away from groups when you get sick, says Dartmouth Hitchcock Medical Center’s Chief Quality Officer Michael Calderwood, MP, MPH, a specialist in infectious diseases. Also, keep washing your hands, even if you feel well, he says.

"We may not be able to eliminate these illnesses altogether, but we certainly can take measures to mitigate them as cases go up," says Calderwood. "And doing what we can to prevent and keep them from getting worse and spreading is even more important as communities bear the impact.

The range of early symptoms

While differences can seem subtle, they do exist, and these can serve as signposts when you first become ill.

"It can be hard to distinguish between illnesses caused by the different respiratory viruses, but generally speaking, the flu often comes on quickly, typically with fever, chills, body aches, fatigue, and a dry cough," says Calderwood.

In contrast to the flu, RSV usually comes on gradually. "People often report congestion, such as a runny or stuffy nose, at times accompanied by sneezing," he says. "Wheezing (a high-pitched whistling with breathing) is also seen more often with RSV than with the other respiratory viruses."

COVID-19 is different from flu or RSV in that it can appear in different forms.

"While we see many of the same symptoms such as cough, fatigue, and headache, COVID-19 may also present with nausea or vomiting, diarrhea, or sudden loss of taste and/or smell. A sore throat also seems to be more common with COVID-19 than with flu or RSV," says Calderwood.

He adds: "In 2025, there is a circulating variant of COVID-19 that has been associated with a painful sore throat that some have described as ‘razor throat.’”

How to treat

When these illnesses are not severe, rest, fluids, and good care can go a long way toward recovery, but it is important to keep a close eye on the severity of any illness. Remember, too, that if you are concerned about how an illness is presenting, consult your doctor.

For RSV

For RSV, it is particularly important to closely monitor adults and children with certain existing medical problems—such as heart disease, cystic fibrosis, and certain lung diseases. The elderly have weaker immune systems overall, so keep a close eye on them.

Babies in their first respiratory virus season can be particularly at risk with RSV, points out Dartmouth Health Children’s Lebanon Section Chief of General Pediatrics, Susanne Tanski, MD, MPH. That’s because not only do people get the sickest when first exposed to the respiratory illness, but a baby’s tiny airways can lead to more severe disease, she says.

For flu

Flu, like all illnesses, should also be monitored. Antiviral drugs may be a treatment option for some, particularly those at higher risk.

Antiviral drugs work best when started early, such as 1 to 2 days after your flu symptoms begin. People at higher risk of flu complications include young children, adults 65 years of age and older, pregnant people, and people with certain medical conditions such as asthma, diabetes, and heart disease. Consult your doctor to find out if antiviral drugs are right for you. You can also visit the Dartmouth Health website for more information on flu treatment.

For COVID-19

The U.S. Food and Drug Administration (FDA) has authorized or approved several antiviral medications to treat mild-to-moderate COVID-19. These therapies are for use in individuals who are at high risk of getting severe disease if infected with COVID-19.

People who are more likely to get very sick include:

  • Older adults (especially those ages 65 years or older, with risk increasing with advancing age)
  • People who are unvaccinated or are not up to date on their COVID-19 vaccinations
  • People with certain medical conditions, such as chronic lung disease, heart disease or a weakened immune system

Most individuals with COVID-19 have mild illness and can recover at home without medical care. These medications are available through a prescription from your primary care provider who can help you decide which treatment is right for you. More information on COVID-19 treatment can be found here.

Prevention

All people, but especially those in high-risk categories, can take precautions to stave off illness by wearing masks, avoiding crowded places, and washing their hands. If you are sick, stay home and keep away from other people.

For COVID-19

The American Academy of Family Practitioners (AAFP) and the American Academy of Pediatrics (AAP)(2025) recommend:

  • All children ages 6-23 months be vaccinated against COVID-19
  • A risk-based, single-dose approach for children and teens 2-18 years
  • Ongoing immunization access for any family wanting to be vaccinated against COVID-19

For pregnant people no matter the trimester and for those breastfeeding, the AAFP and the American College of Obstetrics Gynecologists (ACOG) (2025) recommend COVID-19 vaccination.

For adults aged 75 and older, as well as those aged 50-74 at increased risk, the AAFP supports a one-time RSV vaccine.

If you wish to get vaccinated and don’t meet eligibility requirements, you can still get the vaccine. Please note that some pharmacies may ask that you get a prescription from your doctor.

For Flu

Most people need only one dose of influenza vaccine for the flu season, ideally prior to November. But vaccination should continue throughout the season as long as influenza viruses are circulating.

For RSV

The AAFP supports a one-time RSV vaccine for adults aged 75 and older, and for ages 50–74 at increased risk. During September through January, pregnant patients are advised by AAFP and ACOG to receive the vaccine (Abrysvo) at 32–36 weeks.

The AAP recommends that infants under 8 months without maternal protection should receive the Nirsevimab or Clesrovima immunization.

If you have questions about RSV prevention, please visit our website to learn more.

Concludes Calderwood: "Staying up to date with your vaccines, taking measures to protect and care for yourself and your loved ones, and being aware if you are at higher risk of severe illness, all can go a long way toward mitigating their severity and keeping these illnesses from spreading further this winter season."

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