Medically reviewed by Dr. Gary Rogg, MD 

Sniffles, cough, fever—when respiratory viruses start circulating in the fall and winter, it can be hard to know what’s behind your symptoms. Flu, respiratory syncytial virus (RSV) and COVID-19 share many similarities, but there are also some important differences. Knowing what to look for can help you care for yourself or your child at home and understand when it’s time to call the doctor. 

The Overlap: Shared Symptoms 

Flu, RSV and COVID can all cause symptoms, including: 

• Cough 
• Fever 
• Fatigue 
• Runny or congested nose 
• Sore throat 
• Body aches 
• Headache 

Because of this overlap, it isn’t always possible to tell these viruses apart without a medical exam or test. Here’s what to know about the differences and when you should seek help.  

RSV: Most Concerning for Infants and Older Adults 

RSV is often mild in older children and healthy adults, but it can cause serious illness in infants, young children, older adults and those with weakened immune systems. Watch for: 

• Wheezing or rapid breathing 
• Difficulty feeding in infants 
• Dehydration (fewer wet diapers, dry mouth) 
• Pauses in breathing (apnea) in very young babies 

Flu: Sudden and Intense 

Influenza tends to come on quickly. People often describe waking up and suddenly feeling very sick. Signs may include: 

• High fever and chills 
• Severe body aches 
• Headache behind the eyes 
• Dry cough 
• Extreme fatigue 

COVID: A Wide Range of Symptoms 

COVID symptoms can mimic both flu and RSV, but they often include additional signs such as: 

• Loss of taste or smell (though less common with newer variants) 
• Gastrointestinal symptoms (diarrhea, nausea) 
• Longer-lasting cough and fatigue compared to the flu 

When to Call the Doctor 

Seek medical care if you or your child experiences: 

• Trouble breathing or wheezing 
• High fever that doesn’t come down with medication 
• Severe or worsening cough 
• Dehydration (no urination for over eight hours, dry lips or tongue) 
• Chest pain or pressure 
• Confusion or difficulty staying awake 

For infants under 6 months, contact your pediatrician promptly if you notice any fever or changes in breathing. 

Because the symptoms overlap, testing may be the only way to determine which virus is causing the illness. Your doctor can recommend the right test and treatment plan. 

Protecting Yourself and Others 

Don’t ignore respiratory symptoms—especially in children, older adults or those with underlying health conditions. If you’re unsure what’s causing your illness, a primary care provider or pediatrician can help you get the answers and care you need. 

When it comes to protecting yourself and others, prevention is still the best medicine: 

• Stay up to date on flu and COVID-19 vaccines 
• Ask your doctor about RSV protection for infants and older adults 
• Wash your hands often 
• Cover your coughs and sneezes 
• Stay home when you’re sick 

To make an appointment with a WMCHealth Internal Medicine or Primary Care physician, visit our website or call 914.592.2400.