Illustration of the respiratory syncytial virus (RSV, paler blue). RSV, also known as human orthopneumovirus, causes infections in the lungs and respiratory tract. It is very common in children, but it can also affect adults. The symptoms are usually mild and resemble those of the common cold. The initial stages of infection are controlled by the two major glycoproteins present on the surface of the RSV virion: the attachment glycoprotein (grey) and the fusion glycoprotein (darker blue). The fusion protein is the main target for vaccine development.