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What is RSV?

A medical professional holding a stethoscope to the chest of an infant lying on its back.
RSV can cause seriously illness in infants. (Image credit: Shutterstock)

Respiratory syncytial virus, or RSV, is a very common respiratory virus, particularly among children. Indeed, "by age 2, 90% of people have had at least one infection" with RSV, said Dr. Octavio Ramilo, chief of infectious diseases at Nationwide Children's Hospital in Columbus, Ohio, who studies RSV. But people can catch the virus at any age, and become infected multiple times. 

In healthy children and adults, the virus typically causes mild, cold-like symptoms; but it can cause more serious disease in infants younger than 12 months old, or adults over age 65, according to the Centers for Disease Control and Prevention (CDC). In these more serious cases, the virus spreads from the upper respiratory tract to the lungs, potentially leading to pneumonia, inflammation of the lungs' air sacs (alveoli), or bronchiolitis, inflammation of the lungs' small airway passages.

Infants are particularly at risk for severe disease because of their tiny airways — which, when inflamed, can easily compromise breathing — as well as their immature immune system, Ramilo said. "When you look at the number one cause of hospitalization in the first year of life, the number one is RSV," Ramilo told Live Science. It's a "very problematic pathogen," Ramilo added, and the infection leads to millions of doctor visits and thousands of hospitalizations each year.

Related: The deadliest viruses in history

What are the symptoms of RSV?

Symptoms of RSV often resemble those of the common cold. According to the CDC, typical symptoms include:

  •  Runny nose/congestion 
  •  Coughing 
  •  Sneezing 
  •  Fever 
  •  Decrease in appetite 
  •  Headache 

In infants, additional symptoms can include fussiness and poor feeding, according to the American Academy of Pediatrics (AAP).

Symptoms typically appear within four to six days of exposure to the virus, according to the Mayo Clinic. In severe cases, the Mayo Clinic says symptoms can also include:

  •  Wheezing 
  •  Difficulty breathing or rapid breathing 
  •  A bluish color of the skin caused by lack of oxygen 
  •  Severe cough 

People should seek immediate medical care if they experience difficulty breathing, a high fever or a blueish color of the skin, according to the Mayo Clinic. 

How does RSV spread?

RSV can spread through the air when an infected person coughs or sneezes, or through contact with contaminated surfaces. The virus can survive for up to six hours on hard surfaces, such as toys and doorknobs, and can survive for about 30 minutes on unclean hands, according to AAP. 

Children often spread the virus to others at school or in daycare settings, according to the CDC. Those who are infected with the virus are typically contagious for three to eight days; but people with an immunodeficiency may be contagious for much longer, up to four weeks and even after symptoms clear up.

Is RSV seasonal?

In the U.S., RSV typically circulates from late fall to early spring, but the timing in a given region can vary from year to year, according to the CDC.

In 2020 and 2021, the U.S. saw an unusual trend in RVS infections. According to a report published in July 2021 in the CDC journal Morbidity and Mortality Weekly Report, RSV activity in the U.S. dropped to historically low levels from about April 2020 to April 2021. But when COVID-19 restrictions began to lift in the spring of 2021, RSV surged, leading to an unusual summer spike in RSV infections, the report said.

The reason behind these trends still isn't clear, Ramilo said. Although some experts suspect that measures to reduce the spread of COVID-19 taken in 2020, such as mask-wearing and social distancing, also reduced the spread of RSV, Ramilo said he doesn't think this is the whole story. "I don't think we can explain everything from nonpharmaceutical interventions" like masking wearing and social distancing, said Ramilo, who noted that other respiratory viruses, such as rhinovirus and adenovirus, still circulated in 2020, despite restrictions. 

What is clear is that the summer of 2021 saw a dramatic increase in RSV hospitalizations. "Here, we saw a big increase in July and August," at the same level that's usually seen in December or January, Ramilo said. In 25 years of studying RSV, "this is the first time we've seen an outbreak in the middle of July and August," he said.

Related: 20 of the worst epidemics and pandemics in history

Is RSV the same as COVID-19?

RSV is different from COVID-19. RSV belongs to a family of viruses known as pneumoviruses; whereas SARS-CoV-2, the virus that causes COVID-19, belongs to a group of viruses known as coronaviruses. Since RSV and SARS-CoV-2 are both respiratory viruses, their symptoms can be similar, according to the Mayo Clinic.

It is possible to be infected with both RSV and COVID-19, but such coinfections do not appear to be common, Ramilo said. Doctors have been on the lookout for these coinfections because it's known that children can sometimes be infected with RSV and other coronaviruses that cause the common cold, Ramilo said. But "we haven't seen very many cases [of RSV and COVID-19 coinfections], just a handful," he said.

What are the risk factors for RSV?

According to the CDC and AAP, people at risk for severe RSV infections include:

  •  Premature babies, particularly those born before 29 weeks 
  •  Children younger than 2 years old with congenital heart disease or chronic lung disease 
  •  Children or adults with weakened immune systems due to a medical condition (such as cancer) or medical treatment (such as an organ transplant) 
  •  Older adults, especially those with chronic heart or lung disease 

Each year, RSV is responsible for about 2.1 million visits to the doctor and 58,000 hospitalizations among children younger than 5, according to the CDC. In adults over age 65, the virus causes about 177,000 hospitalizations and 14,000 deaths each year.

 Related: 28 devastating infectious diseases 

How is RSV treated?

There's no specific treatment for RSV. Because RSV is caused by a virus, not a bacterium, antibiotics won't work to treat the infection. Most people who catch RSV get better within a week or two without medical intervention.

Over-the-counter medicines, such as acetaminophen or ibuprofen, can help manage symptoms, such as pain and fever. Children should never take aspirin, according to the CDC. People can also use nasal saline drops and suctioning to help with a stuffy nose, according to the Mayo Clinic. Those with an infection should drink plenty of fluids to stay hydrated. 

RSV may also increase the risk of ear infections in children, according to the AAP. If a child develops a bacterial ear infection, their doctor may prescribe antibiotics.

In rare cases, people with RSV are hospitalized, and their treatment in the hospital may include fluids, additional oxygen or use of a mechanical ventilator to help with breathing.

In the U.S., about 3% of infants with RSV infection need to be hospitalized, Ramilo said. But most are able to go home within two to three days, according to the AAP. 

How is RSV prevented?

Basic hygiene measures can reduce the risk of RSV infection, according to the Mayo Clinic, including:

  •  Frequent hand washing 
  •  Regular cleaning of frequently-touched surfaces, such as doorknobs, as well as children's toys 
  •  Covering coughs and sneezes (with your sleeve rather than your hands.) 
  •  Avoiding contact with sick people 

People who have cold symptoms should steer clear of those at risk for severe disease from RSV, including premature infants and children with underlying heart or lung conditions.

Infants and children at risk for severe disease from RSV may be candidates for a medicine called palivizumab (Synagis), given to prevent RSV infection. Palivizumab is a monoclonal antibody, a type of human-made antibody designed to fight RSV in a similar way to the antibodies people generate when they have a real infection. The drug is given as a shot each month during RSV season, according to the Mayo Clinic. It doesn't help treat RSV, it only prevents it. Parents and caregivers can speak with their doctor to determine if their child would benefit from this medication.

There is currently no vaccine to prevent RSV infection, but that could change soon — multiple companies are testing RSV vaccines in clinical trials. For example, in November 2020, GlaxoSmithKline announced it had started a phase 3 study testing a candidate RSV vaccine for use in pregnant women. In theory, antibodies generated during pregnancy in response to the vaccine could be passed to their babies before birth. 

Work is also under way to develop newer drugs known as extended half-life monoclonal antibodies, which are monoclonal antibodies that stay around longer in the body without being degraded. Such antibodies would require just one dose to provide protection for the first year of life, Ramilo said.

"We think the situation [with RSV] may change dramatically in the next few years as these tools come into practice," Ramilo said. "The future looks so much brighter" for preventing RSV.

Additional resources

  •  Read more about RSV in infants and children, from the American Academy of Pediatrics
  •  Get more details on RSV symptoms and care, from the CDC
  •  Find information on RSV risks and complications, from the Mayo Clinic

This article is for informational purposes only, and is not meant to offer medical advice.  

Rachael Rettner

Rachael has been with Live Science since 2010. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.