Respiratory Syncytial Virus (RSV) and Human Metapneumovirus Infections

RSV and hMPV illnesses manifest similarly. The most recognizable clinical syndromes are bronchiolitis (more common) and pneumonia (rare).

These illnesses typically begin with upper respiratory symptoms and fever and then may 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. Decreased breath sounds may occur in children with pneumonia.

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

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

• Sometimes rapid antigen tests, nucleic acid amplification testing (NAAT) with 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 during RSV season.

Because antiviral treatment is not typically recommended, a specific laboratory diagnosis is not usually necessary for patient management. Rapid antigen tests and molecular diagnostic tests (NAAT with RT-PCR) with a high sensitivity and specificity 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 cultures may also be performed, but because growth and reading of the organism are delayed are less likely to be useful for management. However, a laboratory diagnosis may facilitate hospital infection control by allowing for isolation of children infected with the same virus.

• Supportive care

The treatment of RSV and hMPV infections is supportive and includes supplemental oxygen and hydration as needed (see treatment of bronchiolitis).

Glucocorticoids and bronchodilators (1) are generally not helpful and are not recommended.

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

Nirsevimab and clesrovimab (monoclonal antibodies to RSV) are intended for use as a preventive measure for RSV and are not effective for treatment.Nirsevimab and clesrovimab (monoclonal antibodies to RSV) are intended for use as a preventive measure for RSV and are not effective for treatment.

Nebulized ribavirin, an antiviral medication with activity against RSV, has marginal efficacy, is potentially toxic to health care professionals, and is not recommended except for infection in patients who are severely immunocompromised (2). Limited evidence suggests there may be a mortality benefit in immunocompromised patients, particularly those with hematologic cancer and/or in those who have received a hematopoietic stem cell transplant (3, 4).

The clinical benefit of RSV immune globulin on reducing length of hospitalization or in preventing mortality is uncertain, and the quality of evidence supporting this recommendation in one study was low (5).

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

For infants whose mothers did not receive the RSV vaccine during pregnancy, the American Academy of Pediatrics (AAP) and the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) recommend administration of a long-acting monoclonal antibody to prevent RSV-associated lower respiratory tract infection (1–3). The rationale for this approach is based on the efficacy and safety of these monoclonal antibodies and the need to reduce RSV-related hospitalizations in infants.

Nirsevimab and clesrovimab are monoclonal antibodies used for RSV prophylaxis in infants and/or young children in the United States. RSV antibodies are not needed for most infants if Nirsevimab and clesrovimab are monoclonal antibodies used for RSV prophylaxis in infants and/or young children in the United States. RSV antibodies are not needed for most infants ifRSV vaccination was given to the mother in pregnancy. Nirsevimab and clesrovimab are preferred first-line agents in infants < 8 months. Nirsevimab is recommended for high-risk children 8 months through 19 months of age. The monoclonal antibody palivizumab is no longer manufactured (4).

Nirsevimab,Nirsevimab, a long-acting monoclonal antibody, is recommended for the prevention of RSV in the following infants and young children (1, 5–7):

• 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 neonates (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 > 1 dose of nirsevimab (1 dose in their first RSV season and 1 dose in their second RSV season). Children who receive Only children who meet high-risk criteria should receive > 1 dose of nirsevimab (1 dose in their first RSV season and 1 dose in their second RSV season). Children who receivenirsevimab 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 starts, which is typically October 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 (typically through the end of March in most of the continental United States).

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

ClesrovimabClesrovimab is another long-acting monoclonal antibody recommended for use in infants < 8 months of age whose mothers are not protected by maternal RSV vaccination (2). In a multicenter randomized trial, a single dose of the antibody, given before or during the first RSV season, has been found to be efficacious in reducing both medically attended RSV-associated lower respiratory tract infections and hospitalizations in preterm and full-term infants who are < 8 months of age (8). Clesrovimab is generally well tolerated, with a safety profile comparable to that of placebo.

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

For information on available RSV vaccines for older adults and pregnant women, see Respiratory Syncytial Virus (RSV) Vaccine. One of the currently available RSV vaccines (Recombinant RSVpreF) is indicated for pregnant patients at 32 to 36 weeks gestation from September through January in most of the continental United States. Several maternal, pediatric, and adult RSV vaccines are in development in clinical trials (9).