If you’re experiencing a cough, a fever, congestion or fatigue, it can be difficult to tell which virus is causing your symptoms. While both Respiratory Syncytial Virus (RSV) and Influenza (flu) fall under the category of upper respiratory tract infections (URTIs), they differ in symptom patterns, infectious periods, risk factors and potential complications. Recognising these distinctions can help individuals make informed decisions regarding testing, treatment and preventive measures.  

RSV is a common respiratory virus that infects the airways, lungs, and middle ear. Fever, runny nose, coughs and headaches are among some of the most common symptoms that develop in someone with RSV. Symptoms resemble those of a common cold. 

Influenza is a contagious respiratory illness caused by influenza viruses, primarily influenza A and B. One of the most distinguishing features it has from RSV is its sudden (more acute) onset of symptoms. This may lead to illnesses such as fever, chills and muscle aches, as well as profound fatigue.

The incubation period refers to the time between exposure to a virus and the onset of symptoms. 

• RSV: 4-6 days (range approximately 2-8 days) 
• Influenza: About 2 days (range 1-4 days) 

Influenza symptoms tend to develop more rapidly after exposure, whereas RSV symptoms may take several days to become apparent. 

Understanding how long someone can spread a virus is crucial in preventing transmission to those around you.  

Both RSV and influenza can spread before symptoms start to appear, which increases the risk of an outbreak.  

• RSV: Usually 3-8 days; some infants and immunocompromised individuals remain contagious for up to 4 weeks 
• Influenza: From 1 day before symptoms begin until 5-7 days after becoming ill. 

While anyone can become infected with RSV or influenza, certain groups are more likely to develop serious complications. 

• Infants, particularly those younger than 12 months  
• Premature infants  
• Children with congenital heart disease or chronic lung conditions  
• Adults aged 65 years and older  
• Individuals with immunocompromising conditions  
• Patients with chronic heart or lung disease  

RSV is the most common cause of bronchiolitis (inflammation of very small airways) and pneumonia in children younger than 1 year of age.  

• Adults aged 65 years and older  
• Children younger than 5 years, particularly those under 2 years old  
• Pregnant individuals  
• Individuals with chronic conditions such as asthma, diabetes, heart disease or kidney disease  
• People with weakened immune system  

Vaccines are available for both RSV and influenza, providing an effective means of reducing the risk of infection, severe disease, and hospitalisation in vulnerable populations.

For most children and adults with RSV, treatment focuses on symptom management rather than directly targeting the virus. Recommended measures include:  

• Rest and hydration 

• Fever and pain relief medications 

• Nasal saline and suctioning for infants 

• Monitoring for breathing difficulties 

Patients with severe illness may require hospitalization for oxygen therapy, intravenous fluids, or respiratory support. Antiviral treatment with ribavirin is generally reserved for selected high-risk or severely immunocompromised patients and is not routinely used in most cases. 

Unlike RSV, influenza can be treated with antiviral medications that directly inhibit viral replication. Common options include:

• Oseltamivir (Tamiflu^®) 
• Zanamivir (Relenza^®) 
• Baloxavir marboxil (Xofluza^®) 

These medications are most effective when started within 48 hours of symptom onset and may reduce symptom duration and the risk of complications, particularly in high-risk individuals. Supportive care remains important, but antiviral therapy plays a much larger role in flu management than in RSV treatment. 

RSV and influenza are common respiratory viruses that often circulate during the same season, but they are distinct illnesses. RSV usually develops gradually with cold-like symptoms, while influenza often causes a sudden fever, body aches, and significant fatigue.

Early medical assessment can help ensure the right treatment and reduce the risk of complications. If you think you may have RSV or the flu, consult your GP.

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