RSV

Reviewed by Ann Dietrich, MD, FAAP, FACEP 

Key Takeaways  

Respiratory syncytial virus (RSV) remains a major cause of seasonal respiratory illness across the age spectrum. Although infection is often mild and self-limited in otherwise healthy adults, RSV is also a leading cause of infant hospitalization in the United States and a significant driver of hospitalization and death in older adults and patients with high-risk comorbidities. In most regions of the United States, RSV circulation begins in the fall, peaks in the winter, and wanes in the spring, although local timing varies by year.  

Symptoms of RSV

RSV usually presents as a cold-like illness. Common symptoms include runny nose, congestion, decreased appetite, cough, sneezing, fever, and wheezing. Symptom onset generally occurs four to six days after exposure. Unlike influenza, RSV symptoms often evolve in stages rather than appearing all at once. Most infections resolve within one to two weeks, but lower respiratory tract involvement can develop in susceptible patients.  

In adults, RSV frequently causes an upper respiratory syndrome with cough and congestion, but it can progress to pneumonia or trigger exacerbations of chronic obstructive pulmonary disease (COPD), asthma, or heart failure in vulnerable individuals. In infants and young children, RSV can progress to bronchiolitis or pneumonia, especially in the first months of life.  

RSV in babies versus adults

The clinical phenotype differs meaningfully by age. In infants and young children, early symptoms may include runny nose, reduced feeding, and cough that later progresses to wheezing or increased work of breathing. In very young infants, the presentation may be less overtly “viral” and more nonspecific, with irritability, decreased activity, poor feeding, or apnea. Many infants with RSV do not have fever.  

Adults can have mild symptoms or even be asymptomatic, which contrasts with infants, who almost always manifest some clinical signs. Still, RSV in adults is not benign. Older adults, frail adults, nursing home residents, and adults with chronic cardiopulmonary disease, immunocompromise, or other major comorbidities are at higher risk for severe disease, hospitalization, and death.  

RSV’s contagiousness

RSV is contagious and spreads through direct contact with respiratory droplets, by contact with contaminated surfaces, and by self-inoculation of the eyes, nose, or mouth after touching contaminated hands or objects. People with RSV are usually contagious for three to eight days and can begin spreading virus one to two days before symptoms start.  

That window is not uniform across patient groups. Some infants and some immunocompromised patients can continue shedding and spreading RSV for four weeks or longer, even after symptoms improve. This prolonged infectivity is one reason RSV can spread efficiently in households, childcare settings, and congregate care environments.  

Testing for RSV

RSV cannot be reliably distinguished from influenza, COVID-19, or other viral respiratory infections by symptoms alone. Laboratory confirmation is appropriate when the result will change management, guide cohorting or infection prevention decisions, or clarify diagnosis in high-risk patients.  

The Centers for Disease Control and Prevention (CDC) notes that the most commonly used RSV tests are nucleic acid amplification tests (NAATs), including polymerase chain reaction (PCR)-based assays, and antigen tests. NAATs are highly sensitive and can be used across age groups. Antigen tests provide faster results but are generally less sensitive than NAATs. In practice, molecular testing is especially useful in adults, in whom lower viral shedding can reduce antigen test performance. Multiplex molecular assays may also be helpful when influenza, SARS-CoV-2, and RSV are all in circulation.  

For clinicians, the key takeaway is pragmatic: In a low-risk outpatient with an uncomplicated viral syndrome, RSV-specific confirmation may not alter care. In infants, hospitalized patients, nursing home residents, and older adults who may qualify for influenza or COVID-19 therapy, multiplex respiratory testing can be more clinically useful because symptom overlap is substantial.  

RSV timeline day by day

Patients and families often ask for an “RSV timeline day by day,” but the course is variable and depends on age, prematurity, cardiopulmonary reserve, and immune status. Still, a typical course can be described.

• Exposure to day 0: Incubation is usually four to six days after infection.  
• Days 1-2 of symptoms: Upper respiratory symptoms predominate — rhinorrhea, congestion, sneezing, and cough. Appetite may begin to decline.  
• Days 3-5: Symptoms often intensify. In infants and young children, cough may progress to wheezing, tachypnea, retractions, feeding difficulty, or apnea. This worsening several days into the illness is consistent with the CDC’s observation that symptoms appear in stages and that illness in children may become more severe a few days after onset.  
• Days 6-8: Many otherwise healthy children and adults begin to plateau, but high-risk infants and older adults may declare lower respiratory disease during this window. Contagiousness usually continues through this period.  
• Days 8-14: Most patients improve and recover within one to two weeks, though cough and fatigue can linger. Infants and immunocompromised patients may continue to shed virus beyond clinical recovery.  

Clinically, the most important counseling point is that a child who seems mildly ill on day 1 may worsen on days 3-5, particularly if feeding drops off or work of breathing increases.  

How long can infants spread RSV?

Infants can spread RSV longer than older children and healthy adults. While the usual contagious period is three to eight days, some infants continue spreading virus for four weeks or longer. For infection control counseling, clinicians should avoid using the standard one-week window as an absolute rule in young infants, especially in households with newborns, medically complex children, or immunocompromised contacts.  

Who should get the RSV vaccine ages 50 to 74?

As of February 2026, the CDC recommends a single dose of RSV vaccine for all adults age 75 years and older and for adults ages 50-74 years who are at increased risk of severe RSV illness. The vaccine is not currently annual; adults who already received one dose should not receive another at this time.  

For adults ages 50-74 years, risk factors that support vaccination include chronic cardiovascular disease, chronic lung disease, end-stage renal disease or dialysis dependence, complicated diabetes, neurologic or neuromuscular disease that impairs airway clearance, chronic liver disease, chronic hematologic disease, severe obesity, moderate or severe immunocompromise, and residence in a nursing home. The CDC also allows clinician judgment for frailty, concern for undiagnosed chronic disease, or settings where escalation of care is difficult, such as some remote communities.  

The CDC states that eligible adults may be vaccinated at any time of year, but late summer to early fall, typically August through October in the continental United States, is likely to provide the greatest seasonal benefit.  

How dangerous is RSV for seniors?

RSV is meaningfully dangerous for seniors, particularly adults aged 75 years and older and adults with chronic cardiopulmonary disease, immunocompromise, frailty, or nursing home residence. The CDC estimates that, each year, 110,000-180,000 adults ages 50 years and older in the United States are hospitalized because of RSV. Older CDC burden estimates cited approximately 60,000-160,000 hospitalizations and 6,000-10,000 deaths annually among adults age 65 years and older, underscoring that mortality risk is concentrated in older adults and those with major underlying illness.  

RSV in older adults is not simply a “bad cold.” It can cause pneumonia, precipitate COPD or asthma exacerbations, worsen heart failure, and lead to hospitalization. The CDC surveillance also notes that RSV hospitalization rates are highest among infants and young children, followed by adults age 65 years and older.  

RSV vs. flu vs. COVID-19 symptoms

There is substantial overlap among RSV, influenza, and COVID-19, which is why symptom-based diagnosis is imperfect.  

• RSV often presents with rhinorrhea, congestion, cough, sneezing, fever, decreased appetite, and wheezing. Symptoms may build gradually and, in infants, progress over several days. Wheezing and bronchiolitis are more suggestive of RSV, especially in infants and toddlers, although they are not exclusive to it.  
• Influenza more often has abrupt onset with fever or chills, cough, sore throat, runny or stuffy nose, myalgias, headache, and fatigue. Vomiting or diarrhea can occur, particularly in children.  
• COVID-19 has a broader symptom range, including fever or chills, cough, shortness of breath, sore throat, congestion or runny nose, fatigue, headache, myalgias, nausea, vomiting, diarrhea, and new loss of taste or smell. Loss of taste or smell is not universal and may vary by circulating variant, but it remains more characteristic of COVID-19 than of RSV or influenza.  

For clinicians, the practical distinction is less about trying to identify the virus from symptoms alone and more about recognizing who needs testing, antiviral treatment for influenza or COVID-19, escalation of care, or preventive counseling for high-risk contacts.

Frequently asked questions

What are the first signs of RSV?

The earliest symptoms of RSV are usually similar to those of a common cold and include rhinorrhea, nasal congestion, sneezing, mild cough, and decreased appetite. In infants, early signs may be subtle and include poor feeding, irritability, decreased activity, or apnea rather than overt respiratory distress.

How can clinicians tell RSV apart from flu or COVID-19?

RSV, influenza, and COVID-19 have overlapping symptom profiles, so clinical distinction based on symptoms alone is often unreliable. RSV may be more associated with wheezing and bronchiolitis in infants. Meanwhile, influenza more often has abrupt onset with fever and myalgias, and COVID-19 may include a broader systemic symptom profile, but laboratory testing is often needed when the result will change management.

Is RSV more serious in babies or adults?

RSV can be serious at both extremes of age, but the risk profile differs. In infants, especially those younger than 6 months of age, RSV is a major cause of bronchiolitis and hospitalization. In adults, severe disease is concentrated in older adults, frail patients, nursing home residents, and those with chronic cardiopulmonary disease or immunocompromise.

How long does RSV usually last?

In most patients, RSV illness lasts about one to two weeks. However, cough and fatigue may linger beyond the acute phase. In infants, symptom severity often peaks several days into the illness rather than at onset.

How long can infants spread RSV?

Infants may spread RSV longer than healthy older children and adults. Although many patients are contagious for three to eight days, some infants can shed virus and remain contagious for four weeks or longer.

When should an infant with suspected RSV be evaluated urgently?

Urgent evaluation is warranted for apnea, cyanosis, persistent tachypnea, retractions, nasal flaring, grunting, inability to maintain hydration, lethargy, or worsening respiratory effort. Declining oral intake in a young infant should also prompt concern, particularly during days 3 to 5 of illness when symptoms may intensify.

Should every patient with suspected RSV be tested?

No. RSV testing is most useful when confirmation will influence treatment decisions, infection prevention measures, patient cohorting, or diagnostic clarity in high-risk patients. In otherwise healthy outpatients with mild disease, test results often do not change management.

What is the best test for RSV?

Molecular testing, including NAAT or PCR-based assays, is generally the most sensitive approach and is preferred when diagnostic accuracy matters. Antigen tests offer faster results but have lower sensitivity, particularly in adults.

Who should receive the RSV vaccine between ages 50 and 74?

Adults ages 50 to 74 years should receive a single dose of RSV vaccine if they are at increased risk for severe disease. This includes many patients with chronic heart or lung disease, immunocompromise, end-stage renal disease, complicated diabetes, severe obesity, neuromuscular disease that impairs airway clearance, or nursing home residence.

How dangerous is RSV for seniors?

RSV can be clinically significant in seniors and is associated with hospitalization, pneumonia, exacerbation of chronic cardiopulmonary disease, and death. Risk is highest in adults age 75 years and older, as well as in frail adults and those with major underlying disease.

Is there a specific antiviral treatment for RSV in most adults?

For most immunocompetent adults, treatment is supportive. Management focuses on symptom control, hydration, monitoring for complications, and distinguishing RSV from other viral illnesses for which targeted therapies may exist, such as influenza or COVID-19.

Does RSV always cause fever?

No. Fever may occur, but it is not universal. Infants in particular may have RSV without a documented fever, even when lower respiratory tract disease is present.