Respiratory syncytial virus (RSV) is a single-stranded (ss), negatively oriented (-), unsegmented RNA virus of the Pneumoviridae family (genus Orthopneumovirus). It has a bilayer lipid envelope into which glycoproteins are incorporated, including a fusion (F) and an adhesion (G) protein. There are two groups of RSV, group A and group B. These differ in the antigenic structure of the G protein. Viral strains of both groups circulate simultaneously, but RSV A dominates in most years.

Viral replication occurs in the ciliary epithelial cells of the mucous membranes of the respiratory tract. Syncytia formation caused by the F protein and the body’s immune response reversibly damage the epithelia. The resulting cellular detritus, migrating nonspecific and specific defense cells, and mucus obstruct the bronchi. This favors the development of non-ventilated, but also compensatory over-ventilated lung areas. The infection is usually self-limiting, and the epithelia regenerate within 4-8 weeks.

RSV is a common pathogen of acute upper and lower respiratory tract illness at all ages worldwide and one of the most important causative agents of respiratory tract infections in infants, especially premature infants and young children. In seasonality and symptomatology, RSV infections resemble influenza. Their prevalence in the general population has long been underestimated. However, according to the RKI, current estimates indicate that RSV respiratory infections occur worldwide with an incidence of 48.5 cases and 5.6 severe cases per 1,000 children in the first year of life.