Respiratory Syncytial Virus (RSV) and Human Metapneumovirus Infections

RSV and hMPV illnesses manifest similarly. The most recognizable clinical syndromes are bronchiolitis and pneumonia.

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.

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, 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.

• Supportive care

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

Glucocorticoids and bronchodilators 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, clesrovimab, and palivizumab (monoclonal antibodies to RSV) are primarily intended for use as a preventive measure for RSV and are not effective for treatment.Nirsevimab, clesrovimab, and palivizumab (monoclonal antibodies to RSV) are primarily 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 (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 (1).

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 Centers for Disease Control and Prevention (CDC) and the Advisory Committee on Immunization Practices (ACIP) of the CDC recommend administration of a long-acting monoclonal antibody to prevent RSV-associated lower respiratory tract infection (1, 2). 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, clesrovimab, and palivizumab are monoclonal antibodies used for RSV prophylaxis in infants and/or young children in the United States. RSV vaccines are not needed for most infants if RSV vaccination (Nirsevimab, clesrovimab, and palivizumab are monoclonal antibodies used for RSV prophylaxis in infants and/or young children in the United States. RSV vaccines are not needed for most infants if RSV vaccination (Respiratory Syncytial Virus Vaccine) was given in pregnancy. Nirsevimab and clesrovimab are preferred first-line agents in infants < 8 months. Palivizumab is typically reserved for use in high-risk infants when other agents are not available, largely because of cost and logistical considerations since it is shorter acting and requires monthly dosing (3).

NirsevimabNirsevimab a long-acting monoclonal antibody, is recommended for the prevention of RSV in the following infants and young children (4, 5, 6, 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 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 1 dose of nirsevimab (1 dose in their first RSV season and 1 dose in their second RSV season) (Only children who meet high-risk criteria should receive more than 1 dose of nirsevimab (1 dose in their first RSV season and 1 dose in their second RSV season) (8). 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.

ClesrovimabClesrovimab is another long-acting monoclonal antibody provisionally recommended for use by the Advisory Committee on Immunization Practices (ACIP) of the CDC, for 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 (9). Clesrovimab is generally well tolerated, with a safety profile comparable to that of placebo.

If clesrovimab is administered to an infant for the primary prophylaxis of RSV, then palivizumab must not be administered during the same RSV season. If clesrovimab is administered to an infant for the primary prophylaxis of RSV, then palivizumab must not be administered during the same RSV season.

PalivizumabPalivizumab, also a monoclonal antibody, decreases the frequency of hospitalization for RSV in high-risk infants (10, 11). It should be used only in situations where nirsevimab or clesrovimab are not available.

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 glucocorticoids 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 inter-season RSV activity (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 inter-season RSV activity (12).

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 women 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 (13).