Respiratory syncytial virus

Respiratory syncytial virus (RSV) is a common virus that causes infections of the upper and lower respiratory airways (including the nose, sinuses and lungs). Discovered in 1956, RSV is a ribonucleic acid (RNA) virus that belongs to the family Paramyxoviridae. It is classified into 2 subgroups, RSV-A and RSV-B. Both subgroups tend to co-circulate during each season and both can cause severe disease.

RSV is a leading cause of acute lower respiratory infections and associated hospitalizations in infants and children globally. Nearly all children will have experienced at least one RSV infection by their second year of life. In 2019, there were 33 million RSV-associated cases of acute lower respiratory airway infection, 3.6 million RSV-associated hospital admissions, and 101 400 RSV-attributable deaths in children under 5 years of age. Over 97% of pediatric RSV-related deaths occur in children living in low- and middle-income countries. 

RSV infection in adults is generally mild and presents as low-level upper respiratory airway infections. However, older adults and those with chronic respiratory and/or cardiac conditions are more likely to experience severe disease. RSV-related complications include bronchiolitis (inflammation of the smaller airways in the lung), pneumonia, acute otitis media (infection of the middle ear) and conjunctivitis.

RSV is transmitted via droplets from the nose and throat of infected persons. The average incubation period from infection to symptoms is 4–6 days. Mild upper respiratory tract illness is most common, including symptoms and signs such as runny nose, sore throat, headache, fatigue and fever. In more severe cases, infection can lead to small airway obstruction due to accumulation of dead cells and mucus. Symptoms and signs consistent with lower respiratory tract infection include cough, shortness of breath, rapid breathing and wheezing. Very severe lung infection can result in low oxygen levels, respiratory muscle fatigue and death.

RSV infection and disease occurs in almost all infants before the age of 2 years and most cases of severe disease occur among previously healthy infants. However, some infants are at particularly high risk of severe disease, including very premature infants, and those with underlying lung and heart disease. RSV lower respiratory tract infection in early life might lead to long-term respiratory consequences, including repeat hospitalizations for respiratory illness during infancy, recurrent wheeze and possible impaired lung function into adulthood.

Adults are infected repeatedly with RSV throughout their lifetime. In general, younger adults have mild disease, but elderly people can develop severe disease.

There is currently no treatment for RSV. Infections are usually self-limiting and resolve in 1–2 weeks. Healthy adults and infants infected with RSV typically do not require hospitalization, but medically attended RSV may require supportive care, which includes fever management, hydration, oxygen therapy and nutritional support. 

Several immunization products are currently available to prevent severe RSV disease in infants and elderly adults. To protect infants, there is a vaccine given to pregnant women and persons late in pregnancy, which allows transfer of antibodies against RSV through the placenta to the unborn baby, who is then protected after birth. Another immunization product to protect babies is a long-acting monoclonal antibody that targets the RSV virus and is given as an intramuscular injection to the baby soon after birth. Both products can protect babies for approximately six months. For elderly adults, three RSV vaccines are now available that are equally effective.