Flu vs. RSV — Symptom Comparison
Compare RSV (Respiratory Syncytial Virus) and influenza symptoms. Learn key differences in infants, elderly, and adults. Treatment options and when to seek care.
Medically reviewed by
Dr. Sarah Mitchell, MD
Influenza and Respiratory Syncytial Virus (RSV) are both respiratory viruses that circulate during fall and winter months and share many overlapping symptoms. However, they differ in who they most severely affect, how symptoms progress, and what treatments are available. Knowing the differences can help you seek appropriate care — especially for the very young and very old.
Quick Comparison Chart
| Feature | Influenza (Flu) | RSV |
|---|---|---|
| Most at-risk group | Adults 65+, young children, pregnant women, chronic conditions | Infants under 6 months, premature babies, elderly adults, immunocompromised |
| Onset | Sudden (hours) | Gradual (days) |
| Fever | Common, often high (100–104°F) | Common but usually lower-grade; may be absent in infants |
| Cough | Dry, persistent, can be severe | Wet, productive, often with wheezing |
| Wheezing | Uncommon | Very common, especially in infants and young children |
| Runny nose | Sometimes | Very common — often the first symptom |
| Body aches | Severe, widespread | Mild or absent |
| Fatigue | Extreme, can last 2–3 weeks | Mild to moderate |
| Appetite loss | Common | Common — a key warning sign in infants |
| Breathing difficulty | Possible with pneumonia | Common — hallmark of severe RSV (bronchiolitis) |
| Season | Fall–Winter | Fall–Winter (peaks slightly later than flu in many regions) |
RSV in Infants: What Parents Need to Know
RSV is the leading cause of hospitalization in infants under 1 year old in the United States. According to the CDC, approximately 58,000–80,000 children under 5 are hospitalized with RSV each year. While influenza can also cause severe illness in babies, RSV is far more likely to cause bronchiolitis — inflammation of the small airways in the lungs.
RSV Warning Signs in Babies
- Rapid breathing or belly breathing — chest caving in at the ribs with each breath
- Wheezing — a high-pitched whistling sound when breathing out
- Nasal flaring — nostrils widening with each breath
- Grunting — a rhythmic sound at the end of each exhale
- Poor feeding — taking less than half of normal feeds, or signs of dehydration (fewer wet diapers)
- Lethargy or irritability — baby is unusually sleepy or hard to wake
- Blue-tinged lips or fingernails — a sign of low oxygen requiring immediate emergency care
RSV in Older Adults
The CDC estimates that RSV causes 60,000–160,000 hospitalizations and 6,000–10,000 deaths annually among adults aged 65 and older in the United States — comparable to influenza's toll in this age group. In older adults, RSV often presents as a worsening "chest cold" that can progress to pneumonia, exacerbation of COPD or congestive heart failure, and respiratory failure.
Key difference from flu: RSV in older adults tends to begin with congestion and cough rather than the sudden fever and body aches characteristic of influenza. The cough is typically wetter and more productive.
Can You Have Both Flu and RSV?
Yes — co-infection is possible, especially during peak respiratory virus season. Co-infection can result in more severe illness, particularly in infants and the elderly. Testing is the only way to distinguish them definitively; combination respiratory panels (multiplex PCR) can detect influenza, RSV, and COVID-19 from a single swab.
Treatment Differences
Flu Treatment
- Antiviral medications: Oseltamivir (Tamiflu), zanamivir, baloxavir (Xofluza) — FDA-approved, must be started within 48 hours of symptom onset for maximum benefit
- Annual vaccine: Widely available, reformulated each year for expected circulating strains
- Supportive care: Rest, fluids, over-the-counter fever reducers
RSV Treatment
- No specific antiviral: Unlike flu, there is no widely used antiviral medication for RSV. Ribavirin is occasionally used in severely immunocompromised patients but is not standard
- Supportive care is the mainstay: Hydration, oxygen if needed, suctioning of mucus in infants, mechanical ventilation in severe cases
- Prevention is key: RSV vaccines are now available for adults 60+ and pregnant women (to protect newborns). A monoclonal antibody (nirsevimab/Beyfortus) is recommended for all infants under 8 months entering their first RSV season, and for some high-risk children up to 19 months
Prevention for Both Viruses
- Hand hygiene: Frequent handwashing with soap and water for at least 20 seconds. RSV can live on surfaces for hours
- Avoid touching your face: Both viruses enter through eyes, nose, and mouth
- Clean surfaces: Especially high-touch areas like doorknobs, phones, and toys
- Avoid close contact with sick individuals: Especially important for infants and elderly
- Cover coughs and sneezes: Use a tissue or your elbow
- Stay home when sick: Prevent spreading to vulnerable populations
- Vaccination: Annual flu vaccine for everyone 6 months+. RSV vaccine for eligible adults 60+ and pregnant women
Sources
This article references information from the CDC, WHO, NHS, and peer-reviewed medical literature. Content is reviewed regularly for accuracy. Learn about our editorial policy.