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Respiratory Syncytial Virus (RSV) and Human Metapneumovirus Infections


Brenda L. Tesini

, MD, University of Rochester School of Medicine and Dentistry

Reviewed/Revised May 2023 | Modified Sep 2023

Respiratory syncytial virus and human metapneumovirus infections cause seasonal lower respiratory tract disease, particularly in infants and young children. Disease may be asymptomatic, mild, or severe, including bronchiolitis and pneumonia. Although diagnosis is usually clinical, laboratory diagnosis is available. Treatment is supportive. Passive prophylaxis with nirsevimab is indicated for appropriate children or, when nirsevimab is not available, with palivizumab for specific high-risk infants.

Respiratory syncytial virus (RSV)

RSV is an RNA virus, classified as a pneumovirus. Subgroups A and B have been identified.

RSV is the most common cause of lower respiratory tract illness in young infants and is responsible for > 50,000 hospitalizations annually in the United States in children under the age of 5 years.

RSV is ubiquitous; almost all children are infected by age 4 years. Outbreaks typically occur annually in winter or early spring in temperate climates. However, RSV and other respiratory virus circulation patterns were disrupted during the COVID-19 pandemic (1 Reference Respiratory syncytial virus and human metapneumovirus infections cause seasonal lower respiratory tract disease, particularly in infants and young children. Disease may be asymptomatic, mild... read more ).

Because the immune response to RSV does not protect against reinfection, the attack rate is approximately 40% for all exposed people. However, antibody to RSV decreases illness severity.

Human metapneumovirus (hMPV)

hMPV is a similar but separate virus.

The seasonal epidemiology of hMPV appears to be similar to that of RSV, but the incidence of infection and illness appears to be substantially lower.


  • 1. Olsen SJ, Winn AK, Budd AP, et al: Changes in influenza and other respiratory virus activity during the COVID-19 pandemic–United States, 2020-2021. MMWR Morb Mortal Wkly Rep 70(29):1013–1019, 2021. doi: 10.15585/mmwr.mm7029a1

Symptoms and Signs of RSV and hMPV

These illnesses typically begin with upper respiratory symptoms and fever, then progress over several days to dyspnea, cough, wheezing, and/or crackles on chest auscultation. Apnea may be the initial symptom of RSV in infants < 6 months.

In healthy adults and older children, illness is usually mild and may be inapparent or manifested only as an afebrile common cold. However, severe disease may develop in the following:

  • Patients who are < 6 months old, older adults, or patients who are immunocompromised

  • Patients who have underlying cardiopulmonary or neuromuscular disorders

Diagnosis of RSV and hMPV

  • Characteristic symptoms and signs, particularly during the usual season or a known outbreak

  • Sometimes rapid antigen tests, reverse-transcription–polymerase chain reaction (RT-PCR), or viral culture (all done on nasal washings or swabs)

RSV (and possibly hMPV) infection is suspected in infants and young children with bronchiolitis or pneumonia during RSV season. Because antiviral treatment is not typically recommended, a specific laboratory diagnosis is unnecessary for patient management. However, a laboratory diagnosis may facilitate hospital infection control by allowing segregation of children infected with the same virus.

Rapid antigen tests with a high sensitivity for RSV and other respiratory viruses are available for use in children; nasal washings or swabs are used. These tests are less sensitive in adults. Viral culture may be performed. Molecular diagnostic assays such as RT-PCR have improved sensitivity and are generally available as single or multiplex assays.

Treatment of RSV and hMPV

  • Supportive care

Corticosteroids and bronchodilators are generally not helpful and are currently not recommended.

Antibiotics are reserved for patients with fever, evidence of pneumonia on chest x-ray, and clinical suspicion of a bacterial coinfection.

Palivizumab (monoclonal antibody to RSV) is not effective for treatment.

Inhaled ribavirin, an antiviral medication with activity against RSV, has marginal efficacy, is potentially toxic to health care professionals, and is no longer recommended except for infection in patients who are severely immunocompromised.

Treatment reference

Prevention of RSV and hMPV

Contact precautions (eg, hand washing, gloves, isolation) are important, particularly in hospitals.

Two monoclonal antibodies used for RSV prophylaxis in infants and young children are available in the United States. Nirsevimab is preferred but may not be available to some infants; if it is not available, eligible high-risk infants and children should receive palivizumab.

  • All infants 8 months of age who are either born during or who are entering their first RSV season

  • Children 8 months through 19 months of age who are at increased risk of severe RSV disease and who are entering their second RSV season

Healthy newborns (ie, those who have no increased risk of severe RSV) should receive no more than 1 dose of nirsevimab. Typically, this dose is given during an infant’s first RSV season. Those born at the end of their first RSV season should receive this nirsevimab dose during their second RSV season only if they are still 8 months of age and did not receive nirsevimab during their first RSV season.

Only children who meet high-risk criteria should receive more than one dose of nirsevimab (one dose in their first RSV season and one dose in their second RSV season). Because nirsevimab is preferred, high-risk children who received palivizumab in their first RSV season should receive nirsevimab in their second season, if it is available; if it is not, they should receive palivizumab if indicated. Children who receive nirsevimab should not receive palivizumab in the same RSV season.

High-risk children 8 to 19 months of age include the following:

  • Children with chronic lung disease of prematurity who required medical support any time during the 6-month period before the start of the second RSV season

  • Children who are severely immunocompromised

  • Children with cystic fibrosis who have severe lung disease or whose weight-for-length is less than the 10th percentile

  • Children who are American Indian or Alaska Native

For eligible children, nirsevimab should be given shortly before the RSV season (typically from October through the end of March in most of the continental United States). For infants who did not receive a dose at the start of the season, a dose may be given at any time during the season.

Nirsevimab may be given before the newborn leaves the hospital and simultaneously with other childhood vaccines.

Palivizumab is cost-effective only for infants at high risk of hospitalization, including those with the following characteristics:

  • Born at < 29 weeks gestation and are < 1 year old at the start of RSV season

  • < 1 year old with chronic lung disease of prematurity (gestational age < 32 weeks and 0 days with the need for oxygen therapy for at least 28 days after birth)

  • Chronic lung disease of prematurity in the second year of life and have received within 6 months of RSV season treatment with chronic corticosteroids or diuretics or have had a continued need for oxygen therapy

  • < 1 year old with hemodynamically significant congenital heart disease

Prophylaxis with palivizumab may also be considered for

  • Infants 1 year old who have anatomic pulmonary abnormalities or neuromuscular disorders that impair the ability to effectively clear the upper airways

  • Children < 24 months old who have profound immunocompromise

The first dose of palivizumab is given just before the usual onset of the RSV season. Subsequent doses are given at 1-month intervals for the duration of the RSV season (usually a total of 5 doses). Additional doses may be recommended during a prolonged RSV season or significant interseason RSV activity. (See also the American Academy of Pediatrics' reaffirmed 2014 updated guidance for palivizumab prophylaxis for infants and young children who are at increased risk of hospitalization for RSV.)

Infants who were initially given palivizumab should be given a single dose of nirsevimab if it becomes available before completion of the 5-dose palivizumab series.

Several other maternal, pediatric, and adult RSV vaccines are in development in clinical trials.

Prevention references

  • 1. Hammitt LL, Dagan R, Yuan Y, et al: Nirsevimab for Prevention of RSV in Healthy Late-Preterm and Term Infants. N Engl J Med 386(9):837-846, 2022. doi: 10.1056/NEJMoa2110275

  • 2. Griffin MP, Yuan Y, Takas T, et al: Single-Dose Nirsevimab for Prevention of RSV in Preterm Infants. N Engl J Med 383(5):415-425, 2020. doi: 10.1056/NEJMoa1913556

  • 3. Simões EAF, Madhi SA, Muller WJ, et al: Efficacy of nirsevimab against respiratory syncytial virus lower respiratory tract infections in preterm and term infants, and pharmacokinetic extrapolation to infants with congenital heart disease and chronic lung disease: A pooled analysis of randomised controlled trials. Lancet Child Adolesc Health 7(3):180-189, 2023. doi: 10.1016/S2352-4642(22)00321-2

  • 4. Garegnani L, Styrmisdóttir L, Roson Rodriguez P, et al: Palivizumab for preventing severe respiratory syncytial virus (RSV) infection in children. Cochrane Database Syst Rev 11(11):CD013757, 2021. doi: 10.1002/14651858.CD013757.pub2

  • 5. The IMpact-RSV Study Group: Palivizumab, a humanized respiratory syncytial virus monoclonal antibody, reduces hospitalization from respiratory syncytial virus infection in high-risk infants. Pediatrics 102(3):531–537, 1998.

  • 6. Melgar M, Britton A, Roper LE, et al: Use of Respiratory Syncytial Virus Vaccines in Older Adults: Recommendations of the Advisory Committee on Immunization Practices—United States, 2023. MMWR Morb Mortal Wkly Rep 72:793–801, 2023. doi: 10.15585/mmwr.mm7229a4

  • 7. Papi A, Ison MG, Langley JM, et al: Respiratory Syncytial Virus Prefusion F Protein Vaccine in Older Adults. N Engl J Med 388(7):595-608, 2023. doi: 10.1056/NEJMoa2209604

  • 8. Walsh EE, Pérez Marc G, Zareba AM, et al: Efficacy and Safety of a Bivalent RSV Prefusion F Vaccine in Older Adults. N Engl J Med 388(16):1465-1477, 2023. doi: 10.1056/NEJMoa2213836

  • 9. Kampmann B, Madhi SA, Munjal I, et al: Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants. N Engl J Med 388(16):1451-1464, 2023. doi: 10.1056/NEJMoa2216480

Key Points

  • Respiratory syncytial virus (RSV) and human metapneumovirus usually cause a syndrome of bronchiolitis, but pneumonia may occur.

  • Diagnosis is usually clinical, but testing, including rapid antigen tests and molecular assays (eg, reverse-transcription–polymerase chain reaction), is available.

  • Give supportive treatment; corticosteroids, bronchodilators, nirsevimab, and palivizumab are not recommended.

  • Inhaled ribavirin may be useful for RSV but is potentially toxic to health care professionals and is now used only in patients with severe immunocompromise.

  • Before the RSV season, give nirsevimab to all appropriate children; if nirsevimab is not available, give palivizumab to specific high-risk infants.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Drug Name Select Trade
Copegus, Moderiba, Rebetol, RibaPak, Ribasphere, Ribasphere RibaPak, RibaTab, Virazole
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