Respiratory syncytial virus, or RSV, is a common respiratory virus that spreads seasonally. A new drug and several vaccines that prevent the infection have recently come to market.
Here's what you need to know about the three new shots — two vaccines and one injectable drug — that were recently approved by the Food and Drug Administration (FDA) to fight RSV.
Related: Who should get the new COVID vaccines? What to know about the 2023-2024 shots
How serious is RSV?
Most people who contract RSV develop only cold-like symptoms, like a runny nose, decreased appetite, coughing and sneezing. Mild infections usually resolve without medical treatment. However, RSV can be severe and potentially fatal in infants, young children and older adults.
RSV season typically runs from fall to spring, although its timing has been disrupted in recent years due to the COVID-19 pandemic. Every year in the U.S., the virus leads to approximately 2.1 million doctor's visits among children younger than 5 and about 58,000 to 80,000 hospitalizations in the same age group, the CDC estimates. It's the most common cause of hospitalization in infants, and annually, 100 to 300 children under 5 die from the infection in the U.S.
The children at highest risk include premature babies, infants, children under age 2 who were born with heart disease or have chronic lung disease, and children with weakened immune systems or neuromuscular disorders.
Among adults ages 65 and older, RSV leads to 60,000 to 160,000 hospitalizations each year and about 6,000 to 10,000 deaths in the U.S. Older adults at the highest risk include those with chronic heart or lung disease, those with weakened immune systems, and those living in nursing homes or long-term care facilities. RSV infections in this age group can also worsen existing conditions, like chronic obstructive pulmonary disease (COPD) and congestive heart failure.
Is there a vaccine for RSV?
Yes, there are two FDA-approved vaccines for RSV — one for older adults, and one for both older adults and pregnant people.
The FDA approved the first-ever RSV vaccine in May 2023. The shot, called Arexvy and made by the pharmaceutical company GSK, is approved for adults ages 60 and older.
The vaccine contains an adjuvant, a substance that revs up the immune system, and a lab-made version of a protein found on the surface of the virus. The virus uses this fusion, or "F" protein, to break into cells. The shot trains the immune system to recognize what the F protein looks like in its "prefusion" form, the shape it's in before it infects cells.
The second RSV vaccine approved by the FDA is called Abrysvo. Made by Pfizer, the shot was approved for older adults in May 2023 and for pregnant people in August 2023. Like Arexvy, Abrysvo contains lab-made perfusion F proteins. Neither vaccine contains preservatives, according to their drug labels .
How effective are the RSV vaccines?
In older adults, GSK's Arexvy and Pfizer's Abrysvo offer similar protection against RSV-associated "lower respiratory tract disease" (LRTD), meaning infections that affect the lungs.
In the first RSV season after vaccination, GSK's Arexvy lowers the chance of RSV-related LRTD by 82.6% and the risk of having to see a doctor for LRTD by 87.5%. A year after receiving one dose of vaccine, participants entered their second RSV season post-vaccination; data collected at that time showed that the shot was still 56.1% effective at preventing LRTD.
By comparison, in the first RSV season, Pfizer's Abrysvo is 88.9% protective against LRTD and 84.6% effective at preventing doctor's visits for LRTD. It's 78.6% protective against LRTD in the second season, based on data from part of a subsequent season, according to a Morbidity and Mortality Weekly Report (MMWR) from the CDC.
In February 2024, Pfizer released additional evidence that one dose of its vaccine is highly protective for two consecutive seasons in older adults.
When given in pregnancy, Abrysvo protects newborns by providing them with anti-RSV antibodies that cross the placenta and likely also crop up in breast milk. Abrysvo is specifically approved for use between week 32 and 36 of pregnancy; in clinical trials, this timing resulted in the most protection for newborns. The babies' risk of severe LRTD was slashed by 91.1% within 90 days of birth and by 76.5% within 180 days. The risk of LRTD of any severity was cut by 34.7% in the first 90 days and 57.3% in the first 180 days.
Who should get an RSV vaccine?
Adults ages 60 and older can get one dose of one of these RSV vaccines after discussing it with their doctor, the CDC says.
"The decision to vaccinate an individual patient should be based on a discussion between the healthcare provider and the patient," the CDC states. "It may be informed by the patient's risk of severe RSV disease and their characteristics, values, and preferences; the healthcare provider's clinical discretion; and the characteristics of the vaccine."
The CDC doesn't say all older adults should get the shot, and instead recommends parsing risks and benefits of the shot with a doctor. That's partly because six cases of "inflammatory neurologic events" were reported in clinical trials of the vaccines. These included cases of Guillain-Barré syndrome, a condition in which the immune system attacks the nerves, and acute disseminated encephalomyelitis, which causes swelling in the brain and spinal cord, according to the CDC's MMWR.
Still, both RSV vaccines were deemed very safe in clinical trials with tens of thousands of people, and their most common side effects were mild. Given how few people experienced the inflammatory neurologic events, it's currently unclear if these conditions occurred by chance or if the shots somehow raised their likelihood.
"Until additional evidence becomes available from postmarketing surveillance clarifying the existence of any potential risk, RSV vaccination in older adults should be targeted to those who are at highest risk for severe RSV disease and therefore most likely to benefit from vaccination," the MMWR states.
Regarding using Abrysvo in pregnancy, the CDC has recommended that, during RSV season, pregnant people should get one dose of RSV vaccine between weeks 32 and 36 of gestation. The agency noted that most newborns likely need protection from the prenatal vaccine or from an antibody drug (as described later in the article), but not both.
"However, for example, if a baby is born less than two weeks after maternal immunization, then a doctor may recommend that the baby also receive the infant immunization," the CDC added.
Do you get vaccinated for RSV as a child?
No. There is no approved RSV vaccine for children.
However, newborns will get indirect protection in their early months of life if their parents receive an RSV vaccine during pregnancy. This protection comes from RSV-fighting antibodies that pass through the placenta. The shot doesn't result in a permanent "memory" of RSV in the child's immune system, like a vaccine given in childhood would.
Is there a drug to prevent RSV in children?
Yes, there are two antibody-based drugs available to protect infants from RSV.
Note that, if a pregnant person gets a prenatal RSV vaccine, their infant likely doesn't need an antibody drug on top of that, the CDC has said. But in select cases — for example, if a baby is born less than two weeks after maternal immunization — their doctor may also recommend an antibody drug.
In August 2023, the FDA approved a drug called Beyfortus (generic name nirsevimab-alip). The shot contains lab-made proteins that mimic antibodies made by the immune system. Called a monoclonal antibody, this type of drug doesn't train a child's immune system to make its own RSV-fighting antibodies, like a vaccine would. Instead it provides a ready-made supply. The one-time shot protects children for about five months, the length of an average RSV season, the CDC states.
The CDC initially recommended that all infants younger than 8 months who are born during, or are just entering, their first RSV season should get a shot of Beyfortus. It also advised that some children between the ages of 8 months and 19 months who are at increased risk of severe RSV, including those with weakened immune systems, should also get a shot for their second RSV season.
However, in October, the CDC slightly tweaked its recommendations for how doctors should use Beyfortus during the 2023-2024 season, because it became clear that the supply of the drug could not meet the high demand. In light of the shortage, the CDC announced in mid-November that more than 77,000 additional doses of Beyfortus would be immediately distributed to help improve availability. In addition, in December, the White House announced that an additional 230,000 doses would be made available in January 2024; these will include both the 50-mg and 100-mg doses of the antibody treatment.
Caregivers should consult a health care provider about which RSV antibody drug is available and right for their child.
In addition to Beyfortus, an older antibody shot against RSV, called Synagis (generic name palivizumab), is available. It was first approved in 1998. However, only children at the highest risk of severe disease, not healthy children, should be given this drug, the CDC recommends.
"Palivizumab is limited to children under 24 months of age with certain conditions that place them at high risk for severe RSV disease," the CDC states. "It must be given once a month during RSV season."
For example, Synagis is recommended for premature babies, especially those with chronic lung disease, and infants with certain heart diseases. This limited usage is partly due to the drug's high cost and the fact that it requires at least one and up to five shots a month during RSV season.
Editor's note: This article was updated on March 1, 2024 to include new information about the durability of the Pfizer shot's protection in older adults. It was originally published on Aug. 24, 2023.
This article is for informational purposes only and is not meant to offer medical advice.
Ever wonder why some people build muscle more easily than others, or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!
