Respiratory Syncytial Virus (RSV) is a highly common, seasonal pathogen that infects the lungs and breathing passages. It is a leading cause of respiratory illness worldwide, particularly in infants and older adults, where it can cause severe disease like bronchiolitis and pneumonia. While the virus has existed for an unknown length of time in nature, the timeline of human knowledge regarding its existence is relatively recent, spanning from its initial isolation in animals to modern preventative strategies.
The Initial Isolation and Identification
The story of the virus’s discovery began in 1956, not in a human hospital, but in a colony of chimpanzees at the Walter Reed Army Institute of Research in Silver Spring, Maryland. These chimpanzees, which were being used in polio research, were experiencing a respiratory illness characterized by cold-like symptoms and nasal discharge. Researchers isolated a new virus from these sick animals and initially named it the Chimpanzee Coryza Agent (CCA).
The initial identification viewed the virus primarily as an animal virus causing a common cold in the primate colony. A laboratory worker who had contact with the animals also developed a similar upper respiratory infection, suggesting the virus could cross into humans. However, it was not yet recognized as a major human health concern, especially for severe illness in children, but rather as an agent causing mild respiratory symptoms.
Recognizing the Human Pathogen
The understanding of the virus shifted dramatically in 1957 when an almost identical agent was isolated from infants with severe respiratory disease in Baltimore. Robert M. Chanock and his colleagues found that the virus isolated from children with illnesses like bronchiolitis and bronchopneumonia was indistinguishable from the Chimpanzee Coryza Agent. This discovery firmly established the agent as a human pathogen responsible for serious illness in young children.
The virus was then formally renamed Respiratory Syncytial Virus, a name derived from its characteristic appearance in cell culture. When the virus infects cells in a laboratory setting, it causes the formation of large, multinucleated structures called syncytia, fusing multiple individual cells together. Studies shortly after the discovery revealed that about 80% of children had developed antibodies to the virus by age four, confirming its widespread prevalence. This marked the medical community’s realization of the virus’s public health burden, particularly in the pediatric population.
Decades of Prevention and Management Efforts
Once RSV was recognized as a major cause of lower respiratory tract disease in infants, prevention efforts began in the 1960s. Early vaccine development met a significant setback involving a formalin-inactivated RSV (FI-RSV) vaccine candidate. Children who received this vaccine and were later exposed to the wild-type virus developed a more severe form of the disease, a phenomenon known as enhanced respiratory disease. This outcome led to a halt in vaccine research and instilled caution in the field for decades.
Attention turned to passive immunization in the 1990s as a preventative approach for the most vulnerable infants. This led to the development and introduction of the monoclonal antibody palivizumab (Synagis) in the late 1990s. Palivizumab offers passive protection, given as a monthly injection during the RSV season, to high-risk infants such as those born prematurely or with certain heart or lung conditions. This was the first major preventative step, though its high cost and monthly administration limited its use to a small fraction of the birth cohort.
The last few years have seen the culmination of decades of research, leading to major breakthroughs that offer protection to nearly all infants. In 2023, new preventative options became available, including an RSV vaccine for pregnant individuals, which allows a mother to pass protective antibodies to her fetus before birth. Simultaneously, a new long-acting monoclonal antibody was approved for all infants and young children entering their first RSV season. These developments represent a significant shift from the limited prophylaxis of the past toward widespread prevention against severe RSV disease.