Open Outbreak

Respiratory syncytial virus

Also known as: RSV, human respiratory syncytial virus, hRSV, human orthopneumovirus

Respiratory syncytial virus, or RSV, is a very common virus that infects the nose, throat, and lungs. It spreads between people through respiratory secretions and close contact. Most infections look like a cold, but RSV can also move into the lower airways and cause bronchiolitis or pneumonia, especially in babies, older adults, and people with weak immune systems or chronic heart or lung disease. Recent reviews describe RSV as a major cause of illness worldwide and an important cause of infant mortality and severe disease in older adults. Prevention has changed quickly in the past few years. Reviews published in 2023 and 2024 report that vaccines are now approved for older adults, and that a maternal vaccine and a long-acting monoclonal antibody are approved in some countries to protect infants. Treatment for most people is supportive, such as oxygen and fluids when needed. This is not a disease that appears in WHO Disease Outbreak News often, but seasonal surges can still put heavy pressure on hospitals.

Key facts

TransmissionPerson to person through respiratory secretions and close contact; spread in households and healthcare settings is recognized.
Incubationunknown
Case fatalityunknown; available retrieved sources describe substantial mortality burden in infants and older adults but do not give a single case-fatality figure.
Reproduction numberunknown
VaccineAs of 2024 reviews, vaccines are approved for older adults, and a maternal vaccine is approved in some settings to help protect infants.
TreatmentMainly supportive care. A 2023 review says current therapy is still mostly supportive; monoclonal antibodies are used for prevention rather than routine treatment.
ReservoirHumans
Endemic regionsWorldwide, with seasonal circulation.

Transmission

RSV spreads from person to person through respiratory secretions. In plain terms, that means virus from the nose and mouth can reach other people during close contact, and contaminated hands or nearby surfaces can also matter. A general review on respiratory viruses says transmissibility and mode of spread vary by virus, but close-range respiratory spread is a core pathway for these infections. Infection-control guidance retrieved in this session also treats RSV as a pathogen that needs isolation precautions in healthcare settings, which supports the importance of contact and respiratory spread. RSV is common enough that it repeatedly moves through households, childcare settings, hospitals, and care homes. The retrieved sources do not give a firm incubation-period number or a settled basic reproduction number for a public reference page, so those figures are best listed as unknown here rather than guessed.

Symptoms and severity

For many people, RSV causes a mild upper-respiratory illness that resembles a cold. The concern is that it can also infect the lower airways and lead to bronchiolitis or pneumonia. The burden is not spread evenly. Reviews returned here describe RSV as a major cause of illness in young children and a major cause of morbidity and mortality in older adults, especially people [age] years and above. Infants, especially very young infants, and people with immune problems or underlying heart or lung disease are among the groups most likely to become seriously ill. The literature found in this session does not provide one simple case-fatality percentage that would apply across ages and settings, and those rates vary a lot by access to care and by risk group. Because of that, a single fatality number would be misleading on this page. The safest summary is that most cases are mild, but severe and sometimes fatal disease does occur.

Treatment and vaccines

Treatment for RSV is mainly supportive. That means helping the patient get through the illness safely, for example with oxygen, fluids, and hospital care when breathing is hard. One 2023 review found in this session states that current therapy is still mostly supportive. Prevention has improved much faster than treatment. Reviews from 2023 and 2024 report that RSV vaccines are now approved for older adults, and that a protein-based maternal vaccine and a long-acting monoclonal antibody are approved to protect infants in some countries. The monoclonal antibody nirsevimab is described as a major public health advance for infant protection, and palivizumab remains part of the prevention landscape in some high-risk groups. These products do not mean RSV is solved everywhere: access, cost, rollout, and supply still shape who benefits. The retrieved sources do not support a claim of a widely used RSV-specific curative antiviral for the general public, so that should not be overstated.

Where it occurs

RSV occurs worldwide. The sources retrieved here describe it as a major global public-health problem rather than a virus limited to one region. It is seasonal, but the timing of the season can differ by country and climate. In temperate settings, RSV usually comes in seasonal waves; in tropical and subtropical areas, patterns can be different and sometimes less sharply defined. The 2022 perspective found in this session says the COVID-19 pandemic changed RSV seasonality patterns, showing that the timing of RSV activity can shift when population mixing and control measures change. That matters because health systems often plan pediatric and older-adult respiratory care around expected seasonal peaks. This page has no evidence from WHO Disease Outbreak News of a special international RSV outbreak notice, which fits with RSV being mainly a recurring seasonal virus rather than a WHO outbreak-news event. Even so, its routine yearly burden can be large, especially for hospitals caring for infants and older adults.

Recent history

On this site, the archive count supplied with the request is zero WHO notices since 1996, and the history tool also returned no archived events for the pathogen key. A search of WHO Disease Outbreak News in this session found no titles containing “respiratory syncytial.” That does not mean RSV is unimportant. It means RSV is usually tracked through seasonal surveillance and burden studies rather than through WHO outbreak notices. The recent scientific picture is that RSV has entered a new phase. Reviews from 2023 and 2024 describe a rapidly changing prevention landscape, with approved vaccines for older adults and new infant-protection options through maternal vaccination and long-acting monoclonal antibodies. Another recent paper found here says RSV seasonality shifted during and after COVID-19 control measures, which helps explain why some countries saw unusual timing of RSV surges in the early 2020s. In short, the recent history is less about one dramatic outbreak and more about changing seasonal patterns and new prevention tools.

What to watch

The main signals to watch are practical public-health ones. First, watch for RSV surges appearing outside the usual season or in places with unusual timing, because that can catch hospitals short of beds, staff, oxygen, and pediatric capacity. Second, watch for spread into groups with higher risk of severe disease, especially very young infants, older adults, and people with weakened immune systems. Third, watch whether the new prevention tools actually reach people: supply shortages, high cost, or uneven rollout of maternal vaccination, older-adult vaccines, or infant monoclonal antibody programs would make RSV more concerning. Fourth, watch for signs that protection is weaker than expected in the field, since recent reviews emphasize that global access and implementation are now the key challenges. Finally, because RSV is already a human virus spread by close contact, the important warning sign is not a shift to human transmission but a rise in burden, severity, or health-system strain in new settings or age groups.

Updated