Clinical Overview of RSV

What to know

  • RSV usually causes mild symptoms, but can cause severe illness in infants, some young children, and older adults.
  • CDC recommends a single dose of RSV vaccine to protect all adults ages 75 and older and adults ages 60-74 who are at increased risk of severe RSV.
  • To protect infants and some young children, CDC recommends an RSV monoclonal antibody (nirsevimab) for babies, or the maternal vaccine (Pfizer’s ABRYSVO) for pregnant people during weeks 32-36 of pregnancy.


Respiratory syncytial virus (RSV) is recognized as one of the most common causes of childhood illness and is the most common cause of hospitalization in infants. It causes annual outbreaks of respiratory illnesses in all age groups. In most regions of the United States, RSV season starts in the fall and peaks in the winter, but the timing and severity of RSV season in a given community can vary from year to year.

Healthcare providers should consider RSV in the differential diagnosis of patients with respiratory illness, particularly during the RSV season. For more information about recommended infection prevention and control practices in healthcare settings, see CDC's 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings.

CDC recommends RSV vaccination for all adults ages 75 and older and adults ages 60-74 who are at increased risk of severe RSV. To protect infants from severe RSV, CDC recommends an RSV vaccine for pregnant people or a monoclonal antibody given to the baby after birth. A healthcare provider's recommendation is one of the most important factors influencing a patient's choice to accept a new prevention product or vaccine.

Vaccines for older adults

CDC recommends a single dose of RSV vaccine for:

  • Everyone ages 75 and older
  • Adults ages 60-74 who are at increased risk of severe RSV disease.

Adults ages 60-74 who are at increased risk include those with certain chronic medical conditions, such as chronic lung or heart disease, those with weakened immune systems, and those living in nursing homes or other long-term care facilities.

RSV vaccine is not an annual vaccine, meaning patients do not need a dose every RSV season. Studies are ongoing to determine whether (and if so, when) revaccination may be needed.

For adults who need an RSV vaccine and have not yet received a dose, RSV vaccine can be administered at any time during the year, but the best time to vaccinate patients is in late summer and early fall before RSV usually starts to spread in the community. In most of the continental US, this means the ideal time for vaccination is between August and October.

Immunizations to protect infants

There are two safe and effective immunizations to prevent RSV lower respiratory tract infection in infants. Either a maternal vaccination (Pfizer's ABRYSVO) given to mom during pregnancy or a monoclonal antibody given to the baby is recommended, but administration of both is not needed to protect most infants.

RSV vaccines are not recommended for use in young children.

An RSV vaccine is recommended for pregnant people who are 32–36 weeks pregnant with seasonal administration during September–January in most of the continental United States. In jurisdictions with seasonality that differs from most of the continental United States (e.g., Alaska, jurisdictions with tropical climates), providers should follow state, local, or territorial guidance on timing of administration.

This vaccine provides protection against severe RSV illness to the recipient's baby for up to 6 months of age. However, the infant's protection will wane over time.

Healthcare providers of pregnant people should provide information on maternal vaccines and infant monoclonal antibody products and consider patient preferences when determining whether to vaccinate the pregnant patient or to not vaccinate and rely on administration of nirsevimab to the infant after birth.

Nirsevimab (Beyfortus) is a monoclonal antibody product that can protect infants and some young children from severe RSV disease. It is recommended for:

  • Infants under 8 months old born during – or entering – their first RSV season (typically fall through spring) if their mother did not receive an RSV vaccine, it is unknown whether their mother received an RSV vaccine, or the mother received a vaccine but the infant was born <14 days after vaccination
  • Some children between the ages of 8 and 19 months who are at increased risk of severe RSV disease before their second RSV season. These include:
    • Children who have chronic lung disease of prematurity who required medical support (chronic corticosteroid therapy, diuretic therapy, or supplemental oxygen) any time during the 6-month period before the start of the second RSV season
    • Children with severe immunocompromise
    • Children with cystic fibrosis who have severe disease
    • American Indian and Alaska Native children

Nirsevimab can be considered in rare circumstances even though the mother received an RSV vaccine when, per the clinical judgment of the healthcare provider, the potential incremental benefit of administration is warranted:

  • Pregnant people who may not mount an adequate immune response to vaccination (e.g., people with immunocompromising conditions) or have conditions associated with reduced transplacental antibody transfer (e.g., people living with HIV)
  • Infants who have had cardiopulmonary bypass leading to loss of RSV antibodies
  • Infants with substantially increased risk for severe RSV disease (e.g., hemodynamically significant congenital heart disease, intensive care admission, and requiring oxygen at discharge)

Nirsevimab is administered by intramuscular injection. It is long-acting, providing protection for at least 5 months (the average length of one season), and only one dose is recommended for an RSV season. However, immune protection will wane over time. Another monoclonal antibody, Palivizumab (Synagis), is recommended by the American Academy of Pediatrics (AAP) for administration to infants and young children who are at increased risk of severe RSV disease based on gestational age and certain underlying medical conditions. It is given in monthly intramuscular injections during RSV season. AAP has provided considerations for the 2023–2024 RSV season with regard to palivizumab versus nirsevimab administration for high-risk infants during the same RSV season.

Clinical features

RSV infection can cause a variety of respiratory illnesses and symptoms in infants and young children. It most commonly causes a cold-like illness but can also cause lower respiratory infections like bronchiolitis and pneumonia. Two to three percent of infants with RSV infection may need to be hospitalized. Severe disease most commonly occurs in very young infants. Additionally, children with any of the following underlying conditions are considered at increased risk:

  • Premature infants
  • Infants, especially those 6 months and younger
  • Children younger than 2 years old with chronic lung disease or congenital heart disease
  • Children with suppressed or weakened immune systems
  • Children who have neuromuscular disorders or a congenital anomaly, including those who have difficulty swallowing or clearing mucus secretions
  • Children with severe cystic fibrosis

Infants and young children with RSV infection may have rhinorrhea and a decrease in appetite before any other symptoms appear. Cough usually develops 1 to 3 days later. Soon after the cough develops, sneezing, fever, and wheezing may occur. Symptoms in very young infants can include irritability, decreased activity, and apnea.

Most otherwise healthy infants and young children who are infected with RSV do not need hospitalization. Those who are hospitalized may require oxygen, rehydration, and mechanical ventilation. Most improve with supportive care and are discharged in a few days.

Adults who get an RSV infection usually have mild or no symptoms. Symptoms are usually consistent with an upper respiratory tract infection, which can include rhinorrhea, pharyngitis, cough, headache, fatigue, and fever. Disease usually lasts less than 5 days.

RSV can sometimes also lead to exacerbation of serious conditions such as:

  • Asthma
  • Chronic obstructive pulmonary disease (COPD)
  • Congestive heart failure

Epidemiologic evidence indicates that all adults ages 75 or older and adults ages 60-74 with certain risk factors are at increased risk of severe RSV. The following conditions increase the risk of severe RSV: 

  • Cardiovascular disease (e.g., heart failure, coronary artery disease, congenital heart disease; excluding isolated hypertension),
  • Lung disease (e.g., chronic obstructive pulmonary disease [COPD], emphysema, asthma, interstitial lung disease, cystic fibrosis),
  • Advanced chronic kidney disease (e.g., stages 4–5, dependence on hemodialysis or other renal replacement therapy),
  • Diabetes mellitus with end-organ damage (e.g., diabetic nephropathy, neuropathy, retinopathy, or cardiovascular disease),
  • Severe obesity (body mass index ≥40 kg/m2),
  • Liver disorders (e.g., cirrhosis),
  • Neurologic or neuromuscular conditions (e.g., neuromuscular conditions causing impaired airway clearance or respiratory muscle weakness; excluding history of stroke without impaired airway clearance),
  • Hematologic disorders (e.g., sickle cell disease, thalassemia), and
  • Moderate or severe immune compromise (either attributable to a medical condition or receipt of immunosuppressive medications or treatment).

As well as:

  • Persons who are frail*;
  • Persons who reside in nursing homes or other long-term care facilities providing assistance with activities of daily living; and
  • Persons with other chronic medical conditions or risk factors that a healthcare provider determines might increase the risk of severe disease due to respiratory infection.

*Frailty is a multidimensional geriatric syndrome and reflects a state of increased vulnerability to adverse health outcomes. Although there is no consensus definition, one frequently used tool is the Fried frailty phenotype in which frailty is defined as a clinical syndrome with three or more of the following symptoms present: unintentional weight loss (10 lbs [4.5 kg] in the past year), self-reported exhaustion, weakness (grip strength), slow walking speed, and low physical activity.

Retirement communities and independent living communities for seniors are not considered long-term care facilities. Adults ages 60-74 living in these facilities may still be recommended to receive RSV vaccination if they have certain medical conditions listed above.