Respiratory Syncytial Virus (RSV)

Respiratory syncytial virus (RSV) is a single-stranded, enveloped RNA virus that causes respiratory illness at every stage of life, from a first infection in infancy through repeated reinfections into older adulthood, since immunity after natural infection is incomplete and short-lived. The virus spreads by respiratory droplets and by contact with contaminated surfaces, and in most of Canada follows a seasonal pattern beginning in fall (September/October), peaking in winter (January/February), and tapering through spring (March/April); RSV season in northern latitudes is shifted later, running roughly December through April/May. Its surface fusion (F) protein drives both viral entry and the formation of syncytia (fused, multinucleated cells) in the airway lining, and it is this F protein — specifically its prefusion conformation — that every current RSV vaccine and monoclonal antibody targets.^[1] Most people of any age experience RSV as a self-limited upper respiratory illness. The disease burden that matters clinically concentrates at the two ends of life: in infants, RSV is the leading cause of bronchiolitis and a leading cause of hospitalization in the first year of life; in older adults and people with chronic cardiopulmonary disease or immunocompromise, RSV causes pneumonia and exacerbations of underlying chronic disease. There is no specific antiviral treatment recommended for routine RSV infection at any age — management of active illness is supportive care, and the pharmacotherapy that actually changes outcomes at a population level is prevention: nirsevimab or clesrovimab for infants, palivizumab for a narrower high-risk group, and RSV vaccines for pregnant patients and older or at-risk adults. This is a genuinely fast-moving area of practice — Canada authorized a second infant monoclonal antibody and updated its national immunization guidance for both infants and older adults in 2026 alone — and pharmacists are often a patient's first point of contact for counselling on eligibility and scheduling.

Immunity after natural RSV infection is incomplete and short-lived, so reinfection occurs throughout life — a first infection in infancy does not protect against illness later in childhood, adulthood, or older age.

• Infants: prematurity (under 37 weeks, especially under 29 weeks), age under 6 months at the start of RSV season, chronic lung disease of prematurity (bronchopulmonary dysplasia), hemodynamically significant congenital heart disease, immunocompromise, Down syndrome, neuromuscular disease, congenital airway anomalies, and cystic fibrosis.
• Infants and young children, general: birth shortly before or during RSV season, household crowding, exposure to tobacco smoke, older siblings or daycare attendance, and lack of breastfeeding.
• Older adults: age 75 years and older, residence in a nursing home or other chronic care facility, and general frailty.
• Adults of any age with chronic disease: chronic lung disease (including COPD and asthma), chronic heart disease (including heart failure and coronary artery disease), diabetes mellitus, chronic kidney or liver disease, and immunocompromising conditions (including transplant recipients, hematopoietic stem cell transplant, and active cancer therapy).
• Adults on specific therapies: dialysis and home or chronic oxygen therapy.
• General transmission risk: close contact with young children, congregate living settings, and RSV season (roughly fall through spring in most of Canada).

Differentiating RSV from other common respiratory viruses

RSV, influenza, and COVID-19 commonly circulate together and produce substantially overlapping symptoms; clinical differentiation alone is unreliable, which is why testing matters more for these three viruses than for most other causes of upper respiratory infection.^[2]

Definitive differentiation requires testing — multiplex PCR is preferred where available, since it distinguishes all three from a single sample. Do not assume a diagnosis from symptoms alone when the distinction changes management, such as antiviral eligibility for influenza or COVID-19, or infection-control cohorting decisions in a hospital or long-term care setting.

History

• Onset and progression of symptoms; ask specifically about respiratory distress and feeding/hydration in infants, and about functional decline or worsening of an underlying chronic condition in older adults.
• Age, gestational age at birth for infants, and risk factors for severe disease (see Risk Factors).
• Immunization history — has the infant already received nirsevimab, clesrovimab, or palivizumab this season, or has the adult already received an RSV vaccine, and if not, do they qualify.
• Exposure history — known sick contacts, daycare or school attendance, or a congregate living setting.

Physical examination

• Vital signs, with particular attention to respiratory rate, oxygen saturation, and work of breathing.
• In infants: assess for grunting, nasal flaring, retractions (suprasternal, intercostal, subcostal), wheeze or crackles on auscultation, and hydration status (mucous membranes, fontanelle, capillary refill).
• In older or high-risk adults: assess for signs of pneumonia, decompensated heart failure, or an acute exacerbation of chronic lung disease.

Investigations

• Real-time PCR, including multiplex panels that also test for influenza and COVID-19, is the preferred test where testing is indicated — antigen testing and viral culture have lower sensitivity for RSV.
• Pulse oximetry is reserved for more significant illness (for example, moderate-to-severe bronchiolitis in an infant, or any older or high-risk adult with respiratory symptoms) and is not needed for mild, typical cases.
• Chest imaging is not routinely indicated for typical bronchiolitis or typical RSV illness in an adult — reserve it for atypical presentations, diagnostic uncertainty, or a suspected complication such as pneumonia or effusion.

• Relieve symptoms through supportive care — hydration, oxygenation, and comfort measures.
• Prevent complications: hypoxemia, dehydration, and respiratory failure in infants; pneumonia and exacerbation of chronic cardiopulmonary disease in older or high-risk adults.
• Prevent RSV infection and severe disease before it occurs through appropriate immunoprophylaxis — the single highest-yield intervention available for this condition.
• Avoid unnecessary bronchodilators, corticosteroids, antibiotics, and chest imaging in uncomplicated bronchiolitis.
• Promote antimicrobial stewardship — RSV is viral, and antibiotics are not indicated unless a specific secondary bacterial infection is confirmed or strongly suspected.

• Hand hygiene (soap and water, or 60% or more alcohol-based hand sanitizer) and covering coughs/sneezes to reduce spread — patients are typically contagious roughly 1-2 days before symptom onset and for about 14 days after, sometimes longer in infants and immunocompromised patients.
• Stay home from work, school, or daycare while symptomatic, and avoid visiting hospitals, long-term care facilities, or high-risk individuals (infants, older adults) while contagious.
• Masking is reasonable for a symptomatic individual around others, for a caregiver of someone who is ill, or where required by a setting or personal choice; children under 2 years of age should not wear masks or other face coverings because of the risk of asphyxiation.
• In infants: more frequent, smaller-volume feeds can help maintain total daily intake when an infant is congested or tires easily during feeding; saline nasal drops with bulb or device suction before feeds may help clear secretions.
• Cool-mist humidification and steam have not been shown to improve outcomes in bronchiolitis and are not necessary.
• At-home monitoring in infants: track feeding and wet-diaper frequency, watch for worsening work of breathing, and expect symptoms to often peak in the first 3 days before improving — any deterioration, or no improvement after 3-5 days, should prompt reassessment.^[6]

Pregnancy

Breastfeeding

No RSV-specific restriction applies to breastfeeding — acetaminophen, and ibuprofen outside the pregnancy-specific NSAID cautions above, are both compatible with breastfeeding. Maternal RSV vaccination and infant nirsevimab, clesrovimab, or palivizumab can all be given without interrupting breastfeeding.

Pediatrics

Bronchiolitis-specific supportive care, prevention eligibility, and dosing are detailed throughout this chapter. Readers managing pediatric wheeze or croup alongside RSV season should also see the Croup and Asthma in Infants and Children chapters for overlapping supportive-care and airway-assessment principles, which are not repeated in full here.

Older adults and adults with chronic disease

This is the population targeted by RSV vaccination (see Choose Initial Treatment for the current age/risk-based eligibility tiers) and the population most likely to present atypically (see Recognize the Condition) — maintain a lower threshold for assessment when an older or high-risk adult reports vague symptoms such as fatigue, confusion, or worsening of a chronic condition during RSV season.

Immunocompromised patients

Immunocompromising conditions increase both the risk of severe RSV disease and the population in which specialist-directed ribavirin is occasionally used (see Choose Initial Treatment). Vaccine immune response may be reduced with significant immunosuppression, but vaccination is still generally recommended given the elevated risk of severe disease in this group.

Renal / hepatic impairment

No dose adjustment is required for acetaminophen (within labelled dosing), the RSV monoclonal antibodies, or RSV vaccines based on renal or hepatic function. Use standard caution with ibuprofen in significant renal impairment or dehydration, and avoid acetaminophen doses above the labelled maximum in significant hepatic impairment.

• In infants: reassess urgently if there is no improvement, or any worsening, after 3-5 days — expect symptoms to often worsen over the first 72 hours before improving, and expect cough to potentially persist 2-3 weeks after the acute illness resolves.
• Track receipt of the infant's nirsevimab, clesrovimab, or palivizumab dose, and for palivizumab specifically, confirm monthly adherence throughout the season; confirm maternal vaccination timing (32-36 weeks' gestation) was met if that pathway was used instead.
• In older or high-risk adults: reassess for worsening dyspnea, hypoxemia, or decompensation of an underlying chronic condition.
• No routine test-of-cure or repeat RSV-specific testing is needed after typical, resolved illness at any age.

1. Reassess the diagnosis before assuming treatment failure — a child or adult not improving as expected may have a bacterial superinfection, an alternate or co-infecting virus (influenza, COVID-19), or a different diagnosis entirely, rather than simply prolonged RSV.
2. In an infant with bronchiolitis not improving after 3-5 days, or worsening at any point, refer for urgent reassessment — do not add a bronchodilator, corticosteroid, or antibiotic empirically without a specific indication for one.
3. In an older or high-risk adult with worsening symptoms, reassess for pneumonia, decompensated heart failure, or a COPD exacerbation, and escalate care accordingly.
4. If a scheduled palivizumab dose was missed, resume monthly dosing as soon as possible — protection is reduced for the remainder of the season until the next dose is given.
5. For a patient who develops significant illness despite having received appropriate prevention (nirsevimab, clesrovimab, palivizumab, or vaccination), manage the acute illness per this chapter — prevention reduces the risk and severity of RSV disease but does not eliminate it entirely.
6. For suspected severe RSV lower respiratory tract infection in an immunocompromised or critically ill patient not responding to supportive care, obtain infectious diseases/critical care input regarding specialist-directed ribavirin.

• Using bronchodilators, corticosteroids, or antibiotics for uncomplicated bronchiolitis in an otherwise healthy infant — none are supported by current evidence, and each carries its own risk and cost.
• Ordering chest imaging or bloodwork routinely for typical bronchiolitis when the result will not change management.
• Assuming an older adult's vague symptoms (fatigue, confusion, worsening of a chronic condition) are simply age-related rather than considering RSV, especially during RSV season.
• Treating nirsevimab, clesrovimab, or palivizumab as a treatment for active RSV infection — they are prevention only, given before or at the start of a season's exposure risk.
• Missing eligibility for RSV vaccination in an adult 18-59 years of age with a qualifying chronic condition, because RSV vaccines are often thought of as "an older-adult vaccine" only.
• Assuming palivizumab and nirsevimab/clesrovimab are interchangeable in dosing frequency — palivizumab requires adherent monthly dosing for full-season protection, unlike the single-dose long-acting antibodies.
• Recommending an over-the-counter combination cough/cold product for a child under 6 years of age.
• Missing that maternal RSV vaccination and infant nirsevimab/clesrovimab are largely redundant when both are accessible — nirsevimab/clesrovimab is preferred when available rather than routinely using both.
• Forgetting to ask about RSV immunization status at any pharmacy encounter during RSV season, given how new and rapidly changing this landscape is — pharmacists are well positioned to identify eligible patients who are not yet aware these options exist.

How to use this table: Doses are adult doses and require patient-specific confirmation (renal/hepatic function, weight, allergy history). Pediatric dosing is weight-based per the current product monograph unless stated. Drug pricing is intentionally omitted. Select any drug name to open its complete Pharmasist Drug Database page.

RSV Prevention

Long-acting monoclonal antibodies (infant RSV prevention)

Preferred over palivizumab for most infants — a single dose protects for an entire RSV season.

Monoclonal antibody — monthly dosing (narrower high-risk use)

Reserve for infants who do not have access to nirsevimab or clesrovimab, or specific high-risk situations where monthly dosing is preferred.

RSV vaccines — maternal immunization and older/at-risk adults

All target the prefusion conformation of the RSV F protein; a single dose per indication, with revaccination schedules not yet established.

Symptomatic supportive care

First-line comfort measures for active illness at any age; neither treats the underlying infection.

Antiviral — specialist-directed only

Reserved for severe, laboratory-confirmed RSV lower respiratory tract infection in a hospital setting; not a primary-care- or community-pharmacy-initiated therapy.

Also avoid: over-the-counter cough and cold products (antitussives, decongestants, expectorants) in children under 6 years of age, per product labelling and Health Canada guidance.^[21]