Ask the Experts: RSV (Respiratory Syncytial Virus)

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Respiratory syncytial virus (RSV) is a common respiratory virus, usually causing mild, cold-like symptoms, such as cough, runny nose, sore throat, headache, fatigue, and fever. Though most people recover in a few days, for some people, RSV can cause serious lower respiratory tract infection (LRTI), such as bronchiolitis or pneumonia. RSV is the most common cause of hospitalization in infants in the United States. Older adults, especially those with chronic health conditions and those age 75 and older, are also more likely to develop severe RSV disease and need hospitalization. There is no specific treatment for RSV illness, only supportive care.

RSV causes annual outbreaks of respiratory illness in people of all ages. In the continental United States, RSV typically circulates in the fall and winter months, between October and March, although its seasonality can vary locally from year to year.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Most adults experience a mild upper respiratory tract infection with RSV, with symptoms lasting only a few days. Some adults with RSV develop lower respiratory tract disease, including pneumonia. Because public health surveillance and testing for RSV in adults been limited in the past, our estimates of the burden of RSV disease are not precise and may underestimate the true burden among adults. Among U.S. adults age 65 and older, RSV is responsible for approximately 60,000 to 160,000 hospitalizations and 6,000 to 10,000 deaths each year.

The risk for severe RSV infection increases substantially with increasing age, especially among those who are 75 years of age and older. Risk is also increased for those who have one or more chronic health conditions, including people who are moderately or severely immunocompromised and people who are considered frail or who live in a nursing home or long-term care facility.  Among those with health conditions, the risk of hospitalization goes up significantly with age and among those who have multiple health conditions. To review the specific high-risk conditions that ACIP considers important for vaccination of adults age 50 through 74 years, see this question.

Last reviewed: August 24, 2025

Almost all U.S. infants and toddlers contract RSV illness within the first two years of life. RSV causes a mild respiratory illness in most, with symptoms including cough, runny nose, fever, and fatigue. Illness is more likely to be mild if the child is older at the time of first infection. Infants with RSV infection frequently develop bronchiolitis, a lower respiratory tract disease (LRTD) that can be severe.

RSV LRTD is the leading cause of hospitalization among U.S. infants, who may require supplemental oxygen, treatment for dehydration, or mechanical ventilation. Approximately 50,000–80,000 RSV-associated hospitalizations and 100–300 RSV-associated deaths occur each year among U.S. infants and children younger than age 5 years. The risk of severe RSV disease is increased by prematurity and lung disease, among other health conditions. However, RSV is also the leading cause of hospitalization among healthy, full-term infants. The large majority (almost 80%) of infants and children younger than age 2 who are hospitalized with RSV are otherwise healthy and have no underlying medical conditions.

Some otherwise healthy American Indian or Alaska Native (AI/AN) children experience higher rates of severe RSV disease than the general population. One study found that the incidence of RSV-associated hospitalization among children in their second RSV season in some AI/AN communities was 4 to 10 times higher than that of similar-aged children elsewhere in the United States. AI/AN children living in remote areas may also have difficulty accessing adequate medical care when they develop LRTD.

Last reviewed: August 24, 2025

In most temperate regions of the continental United States and other areas with similar climates, RSV season typically begins in the fall and peaks in the winter, generally circulating between October and the end of March. However, the timing and severity of RSV season in a given community can vary from year to year. RSV seasonality was temporarily disrupted by the COVID-19 pandemic and widespread changes in social interactions and infection control practices (e.g., mask wearing, social distancing).

U.S. states and territories with very different weather patterns from the continental United States (e.g., Alaska, and areas with tropical weather patterns, such as Hawaii, southern Florida, Puerto Rico, and other island territories) may experience very different patterns of local RSV circulation. For this reason, public health authorities in those areas may issue different recommendations for appropriate timing of RSV prevention strategies (vaccines, monoclonal antibodies).

Last reviewed: August 24, 2025

There are three RSV vaccines licensed and recommended in the United States. Each is listed below, along with their FDA-licensed indications:

  • Abrysvo (RSVpreF, Pfizer, originally licensed May 2023): For all adults age 60 years or older, adults age 18 through 59 years with high-risk conditions for severe RSV disease, and during pregnancy from 32 through 36 weeks’ gestation (download the package insert from FDA: www.fda.gov/media/168889/download)
  • Arexvy (RSVpreF3, GSK, originally licensed May 2023): For all adults age 60 years or older, adults age 50 through 59 years with high-risk conditions for severe RSV disease (download the package insert from FDA: www.fda.gov/media/167805/download)
  • mResvia (mRNA RSV, Moderna, originally licensed May 2024): For all adults age 60 years or older, adults age 18 through 59 years with high-risk conditions for severe RSV disease (download the package insert from FDA: www.fda.gov/media/179005/download)

All three may be used as recommended by CDC and ACIP as a single dose for all adults age 75 years or older and for adults age 50 through 74 years with high-risk conditions for severe RSV disease. Only Abrysvo is licensed for use during pregnancy (during 32 through 36 weeks and 6 days’ gestation) for the prevention of RSV disease in infants.

Arexvy and Abrysvo are recombinant protein vaccines that contain the prefusion form of the F protein found on the surface of the RSV virus. The mResvia mRNA vaccine contains mRNA that encodes the prefusion form of the RSV F glycoprotein. The mRNA vaccine temporarily enables some of the vaccine recipient’s own cells to produce the prefusion form of the RSV F protein, causing the immune system to respond by generating antibodies to it. Because none of these vaccines contain live virus, they cannot cause RSV illness.

The GSK vaccine, Arexvy, includes an AS01adjuvant, a chemical designed to enhance the immune response to vaccination. AS01 is the same adjuvant used in GSK’s recombinant zoster vaccine (Shingrix), but Arexvy contains half the amount of adjuvant as a dose of Shingrix. Abrysvo and mResvia vaccines do not contain an adjuvant.

Last reviewed: September 16, 2025

All three RSV vaccines were effective in preventing RSV-associated lower respiratory tract disease (LRTD) in clinical trial participants, over the course of two RSV seasons.

The global clinical trials for RSVPreF3 (Arexvy, GSK) vaccine involved nearly 25,000 participants and some participants were followed for 2 RSV seasons. One dose reduced the risk of laboratory-confirmed RSV-associated LRTD with two or more symptoms by 82.6% during the first RSV season and 56.1% during the second season. In studies of the real-world effectiveness of Arexvy during the 2023–2024 RSV season, the first since licensure of Arexvy, Arexvy was approximately 77% effective in preventing RSV-associated emergency department encounters and 83% effective in preventing RSV-associated hospitalizations in adults 60 and older.

The RSVpreF (Abrysvo, Pfizer) vaccine global clinical trials involved nearly 37,000 participants, and some participants were followed for 2 RSV seasons. One dose reduced the risk of symptomatic, laboratory-confirmed RSV-associated LRTD with 3 or more symptoms by 88.9% during the first RSV season and 78.6% during a partial second season. In studies of the real-world effectiveness of Abrysvo during the 2023–2024 RSV season, the first RSV season since licensure, Abrysvo was approximately 79% effective in preventing RSV-associated emergency department encounters and 73% effective in preventing RSV-associated hospitalizations in adults 60 and older.

The mRNA RSV (mResvia, Moderna) vaccine global clinical trials involved nearly 37,000 participants. One dose reduced the risk of symptomatic laboratory-confirmed RSV LRTD with three or more symptoms by 80.9% in the first season. After a median follow up time of 18.8 months, its efficacy declined to 48.4%. Because mResvia was licensed so recently, real-world vaccine effectiveness against RSV-associated hospitalization and other severe illness cannot yet be estimated.

Few people enrolled in the clinical trials were either frail or of advanced age (80 or older), and none lived in long-term care facilities. People with immunocompromising conditions were excluded from clinical trials. For this reason, the clinical trials did not measure how well the vaccines would work in the people at highest risk of serious RSV disease. However, CDC notes that real-world data for Arexvy and Abrysvo during the 2023–2024 RSV season demonstrated effectiveness in these groups.

Last reviewed: August 24, 2025

Yes.

In studies of the real-world effectiveness of Arexvy during the 2023–24 RSV season, the first since licensure of Arexvy, Arexvy was approximately 77% effective in preventing RSV-associated emergency department encounters and 83% effective in preventing RSV-associated hospitalizations in adults age 60 and older.

In studies of the real-world effectiveness of Abrysvo during the 2023–24 RSV season, the first RSV season since licensure, Abrysvo was approximately 79% effective in preventing RSV-associated emergency department encounters and 73% effective in preventing RSV-associated hospitalizations in adults age 60 and older.

The Moderna mResvia vaccine was first used during the 2024–25 season. Real-world effectiveness data are not yet available.

For additional details, see the CDC MMWR published in August 2024: www.cdc.gov/mmwr/volumes/73/wr/pdfs/mm7332e1-H.pdf.

Last reviewed: August 24, 2025

Currently, protection from serious lower respiratory tract disease (LRTD) after RSV vaccination is expected to last for at least two RSV seasons, but exactly how well it protects over a longer period of time is not yet known. In clinical trials, the ability of the vaccine to reduce the risk of serious lower respiratory tract disease was tested in some people over 2 RSV seasons, and all RSV vaccines provided meaningful protection in the second season.

RSV vaccination is currently recommended as a single dose: revaccination is not yet recommended. ACIP will update its recommendations concerning whether to revaccinate, and when, as more data become available over time concerning how long protection from a single dose lasts and how effective revaccination is in boosting protection. A small study by GSK did not show a meaningful benefit of revaccination with Arexvy just one year after dose 1; however, revaccinating after a longer interval might be helpful. Studies are underway to evaluate the benefit of revaccination at different intervals.

Last reviewed: August 24, 2025

All three RSV vaccines are currently licensed and recommended as a one-time dose for any person. Recommendations for revaccination have not been made. At this time, a pregnant person who receives Abrysvo (Pfizer) during one pregnancy is not recommended to receive Abrysvo during a subsequent pregnancy: in subsequent pregnancies, the baby should receive an RSV preventive antibody after delivery for RSV protection. ACIP will make decisions concerning RSV revaccination as more data become available over time.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Only the RSVpreF vaccine, Abrysvo by Pfizer, is licensed and recommended for one-time use between 32 weeks and 36 weeks 6 days of gestation to prevent RSV-associated lower respiratory tract disease in infants younger than 6 months old. Do not use Arexvy (GSK) or mResvia (Moderna) during pregnancy. If a pregnant person received an RSV vaccine before the current pregnancy, do not use Abrysvo during this pregnancy. Instead, counsel them that a dose of RSV preventive antibody will be needed to protect the infant from RSV after birth.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

ACIP routinely recommends a single dose of any of the three licensed RSV vaccines for all adults age 75 years and older. ACIP also recommends a single dose of any RSV vaccine for adults age 50 through 74 years who are increased risk for serious RSV infection due to specific high-risk conditions, frailty, or high-risk living arrangements (e.g., residents of long-term care facilities). Refer to the question and answer about high-risk conditions for which CDC recommends vaccination among adults age 50 through 74 years for the detailed list.

In April 2025, ACIP voted to lower the age for initiating vaccination of high-risk adults from age 60 years to age 50 years. The recommendation was accepted and made official in the summer of 2025. The indications for those age 50 through 59 years are the same as those published for people age 60 through 74 years. See the detailed MMWR publication of the ACIP recommendation for older adults, including those at high risk beginning at age 60 years here: www.cdc.gov/acip-recs/hcp/vaccine-specific/rsv.html.

Last reviewed: August 24, 2025

Because of the strong association between the risk of severe RSV disease and age, ACIP recommends RSV vaccination of all adults age 75 years or older. ACIP has specified several conditions as reasons for RSV vaccination before age 75 years (age 50 through 74 years) due to their association with a high risk of hospitalization with severe RSV disease compared to otherwise healthy adults of the same age. ACIP voted to lower the youngest age for vaccination of adults at high risk from 60 years to 50 years in April 2025, but the risk groups are unchanged. These conditions are similar to, but not the same as, high-risk conditions specified for pneumococcal or influenza vaccination. An individual’s risk is increased further if they have more than one of the conditions.

  • Non-immunocompromising chronic health conditions:
    • Chronic cardiovascular disease (such as heart failure, coronary artery disease, or congenital heart disease [excluding isolated hypertension])
    • Chronic lung disease (such as chronic obstructive lung disease [COPD], emphysema, asthma, interstitial lung disease, or cystic fibrosis)
    • End-stage kidney disease or dependence on hemodialysis or other renal replacement therapy
    • Diabetes mellitus complicated by chronic kidney disease, neuropathy, retinopathy, or other end-organ damage, or requiring treatment with insulin or sodium-glucose cotransporter-2 (SGLT2) inhibitor
    • Severe obesity (measured as a body mass index of 40 kilograms per meter squared or greater)
    • Chronic liver disease (such as cirrhosis)
    • Neurologic or neuromuscular conditions causing impaired airway clearance or respiratory muscle weakness (such as poststroke dysphagia [swallowing dysfunction], amyotrophic lateral sclerosis [ALS], or muscular dystrophy [excluding history of stroke without impaired airway clearance])
    • Chronic blood disorders (such as sickle cell disease, thalassemia)
  • Moderate or severe immune compromise (due to a medical condition or due to immunosuppressive medications or treatment)
  • Overall frailty (based on an assessment of frailty)
  • Residence in a nursing home or other long-term care facility
  • Other chronic medical conditions or risk factors not specified in this list that a healthcare provider determines might increase the risk of severe disease due to RSV respiratory infection

People age 50 through 74 years who do not have a medical condition or risk factor that increases their risk of severe RSV disease are not recommended to receive RSV vaccine: they should wait to be vaccinated until a high-risk condition develops or until they turn 75, whichever comes first.

 

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

CDC specifies for RSV vaccination the same moderate to severe immunocompromising conditions that require additional doses of COVID-19 vaccines. Below is the CDC description from its website (www.cdc.gov/covid/hcp/vaccine-considerations/immunocompromised.html#cdc_cg_special_populations_section_3-description-of-moderate-and-severe-immunocompromising-conditions-and-treatment).

Moderate and severe immunocompromising conditions and treatments include but are not limited to:

  • Active treatment for solid tumor and hematologic malignancies
  • Hematologic malignancies associated with poor responses to COVID-19 vaccines regardless of current treatment status (e.g., chronic lymphocytic leukemia, non-Hodgkin lymphoma, multiple myeloma, acute leukemia)
  • Receipt of solid-organ transplant or an islet transplant and taking immunosuppressive therapy
  • Receipt of chimeric antigen receptor (CAR)-T-cell therapy or hematopoietic cell transplant (HCT) (within 2 years of transplantation or taking immunosuppressive therapy)
  • Moderate or severe primary immunodeficiency (such as common variable immunodeficiency disease, severe combined immunodeficiency, DiGeorge syndrome, or Wiskott-Aldrich syndrome)
  • Advanced HIV infection (people with HIV and CD4 cell counts less than 200 per cubic milliliter, history of an AIDS-defining illness without immune reconstitution, or clinical manifestations of symptomatic HIV) or untreated HIV infection
  • Active treatment with high-dose corticosteroids (i.e., 20 mg or more of prednisone or equivalent per day when administered for 2 or more weeks), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor necrosis factor (TNF) blockers, and other biologic agents that are immunosuppressive or immunomodulatory (e.g., B-cell-depleting agents)

Factors to consider in assessing the general level of immune competence in a patient include disease severity, duration, clinical stability, complications, comorbidities, and any potentially immune-suppressing treatment.

For additional information about the degree of immune suppression associated with different medical conditions and treatments, refer to the CDC General Best Practice Guidelines for Immunizations section on altered immunocompetence (www.cdc.gov/vaccines/hcp/imz-best-practices/altered-immunocompetence.html) or the Infectious Diseases Society of America policy statement, 2013 IDSA Clinical Practice Guideline for Vaccination of the Immunocompromised Host (https://academic.oup.com/cid/article/58/3/e44/336537).

Last reviewed: August 24, 2025

No. RSV vaccination is not recommended for people his age with hypertension and no other risk conditions. People age 50 through 74 years who do not have a medical condition or risk factor that increases their risk of severe RSV disease are not recommended to receive RSV vaccination at this time.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

In 2023, when RSV vaccines were initially licensed, ACIP recommended use of RSV vaccine for anyone 60 years and older based on shared clinical decision-making, which includes a conversation about individual risks and benefits of vaccination with a healthcare provider. The recommendation was made when there were limited data about how well the vaccine would work in preventing RSV-associated hospitalization or death due to the relatively healthy older adults enrolled in the clinical trials. There was also a question about whether (or how frequently) a person would need revaccination and whether the vaccination might increase the rare risk of Guillain-Barré syndrome. Given these uncertainties, ACIP members felt that people should have the option to choose to receive RSV vaccine or wait until their risk of serious RSV disease escalates, as it does after age 75. Shared clinical decision-making proved time-consuming and difficult to implement for healthcare providers and patients, due to the lack of clarity about who should prioritize RSV vaccination.

Updated evidence on the balance of RSV vaccination benefits and risks led ACIP in June 2024 to make a definitive routine age-based recommendation for adults age 75 years and older, accompanied by a risk-based recommendation for those age 60 through 74 years with specific high-risk conditions. Due to the relatively small benefit of vaccination for healthy people younger than age 75 and the ongoing uncertainty about revaccination, the option for vaccination of people age 60 through 74 years without risk factors for severe RSV disease was removed. In April 2025, ACIP voted to lower the age to initiate vaccination of adults at high risk of serious RSV disease from 60 years to 50 years.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

As long as he remains healthy, let him know that he can wait until age 75 to get an RSV vaccine. Plan to reassess his need for RSV vaccination periodically. If he develops a high-risk condition that puts him at increased risk of severe RSV disease before turning 75, you should vaccinate him at that point.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

No. Only a single dose of RSV vaccine is currently approved and recommended. There is no evidence at this time to determine if or when revaccination would be of value. Available evidence from clinical trials indicates that RSV vaccination provides meaningful protection against severe RSV disease for at least 2 RSV seasons.

People who were vaccinated for RSV during a previous pregnancy and are pregnant again should not receive RSV vaccination for prevention of RSV in their infant. Instead, the infant should be immunized with an RSV preventive antibody after birth.

As more data becomes available, FDA and the ACIP will evaluate the benefit and timing of RSV revaccination and issue updated recommendations as needed.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Yes, coadministration of influenza and RSV vaccines at the same visit is acceptable. CDC has provided the details of available information in its guidance on RSV vaccination of older adults: www.cdc.gov/vaccines/vpd/rsv/hcp/older-adults.html#administration-other-vaxs.

CDC advises that when deciding whether or not to coadminister other vaccines with an RSV vaccine, consider whether the patient is up to date with currently recommended vaccines, the feasibility of the patient returning for additional vaccine doses, their risk for acquiring vaccine-preventable disease, vaccine reactogenicity profiles, and patient preferences.

Last reviewed: September 3, 2025

Pregnant patients between 32 and 36 weeks and 6 days’ gestation during the months of September through January in the United States should get one dose of the Pfizer RSVpreF vaccine (Abrysvo) to protect their babies during their first RSV season after birth. Only Abrysvo is FDA-approved and recommended for pregnant patients. Arexvy (by GSK) and mResvia (Moderna) are not approved and should not be given during pregnancy.

In most of the continental United States, maternal RSV vaccine is recommended only September through January. Those who provide health care to pregnant patients who live in areas with different patterns of RSV seasonality, such as Alaska, Hawaii, parts of Florida, or other jurisdictions outside the continental United States, should follow guidance from state or territorial public health authorities about the timing of RSV vaccination during pregnancy in their regions.

RSV vaccine is only recommended as a single dose; revaccination is not recommended. However, RSV vaccination during one pregnancy is not expected to protect infants resulting from future pregnancies. Therefore, a patient who is currently pregnant and received RSV vaccine before the current pregnancy should be counseled that their infant should be immunized with an RSV preventive antibody for protection against RSV disease after birth.

Last reviewed: August 24, 2025

No. Only the Pfizer (Abrysvo) RSV vaccine is recommended during pregnancy. The GSK RSV vaccine (Arexvy) and the Moderna vaccine (mResvia) are not licensed or recommended for use in pregnancy.

If Arexvy or mResvia is inadvertently administered during pregnancy, do NOT administer a dose of Abrysvo. Instead, CDC recommends that the infant (if younger than 8 months) should be immunized with an RSV preventive antibody product during RSV season (generally October through March in most of the continental United States). Treat the infant in the same manner as an infant born to a mother who did not receive RSV vaccination during pregnancy.

CDC strongly urges that this type of administration error be reported to the Vaccine Adverse Event Reporting System, VAERS (https://vaers.hhs.gov). Prevent administration errors with health care provider training on the different indications for each RSV prevention product (both vaccines and the preventive antibody products for infants) and always check product labels at least three times before administration to verify that the correct product is being administered to the patient. Consider implementing other feasible safeguards in your system (e.g., electronic alerts) to prevent such errors.

Last reviewed: August 24, 2025

No. RSV vaccination during pregnancy is only recommended for pregnant people who have not previously received an RSV vaccine and who are at the recommended stage of pregnancy (32 weeks through 36 weeks 6 days’ gestation) during the recommended time of year (typically September through January). In regions with seasonal patterns of RSV that differ from the continental United States, such as Alaska, Hawaii, or subtropical parts of Florida, follow state or territorial public health guidance on timing, which may differ.

Last reviewed: August 24, 2025

Yes. Pfizer’s RSV vaccine (Abrysvo) may be administered to a previously unvaccinated pregnant person from 32 weeks through 36 weeks and 6 days’ gestation. RSV vaccine should not be administered to someone at 37 weeks’ gestation or beyond.

RSV vaccine should be administered at least 2 weeks before delivery to allow time for the maternal immune system to create antibodies and transfer sufficient antibodies to the fetus for adequate protection after birth. If the gestational age is appropriate, but clinical judgment is that delivery is likely to occur within 2 weeks, it is reasonable to defer vaccination and plan to immunize the infant with an RSV preventive antibody product after delivery. Infants born less than 14 days after maternal RSV vaccination are recommended to be immunized with an RSV preventive antibody product after birth to ensure adequate protection.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Many pregnant people will have a choice about whether to get Abrysvo during pregnancy or to immunize their infant with an RSV preventive antibody product after birth. Those who are previously unvaccinated and between 32 and 36 weeks 6 days’ gestation between September and January, may be vaccinated with Abrysvo or have their infant receive an RSV preventive antibody product soon after birth (preferably within the first week of life if born during a month when RSV preventive antibody product administration is recommended).

It is important to note that both Abrysvo RSV vaccine and RSV preventive antibody products may not be available or an option for all people in all settings. In some facilities or circumstances, only one option might be available: those offered Abrysvo during pregnancy may not wish to defer that option unless they are confident that an RSV preventive antibody product will be available for their infant. Conversely, if the pregnant person received RSV vaccine before the current pregnancy, only an RSV preventive antibody product administered after birth is recommended for RSV prevention. All infants up to 8 months 0 days of age whose mothers were not vaccinated may be given an RSV preventive antibody product when feasible, before or during their first RSV season.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Yes. VFC-eligible pregnant adolescents younger than age 19 may receive VFC-funded Abrysvo (Pfizer) RSV vaccine during pregnancy, if indicated, in VFC-participating facilities. Contact your state or territorial immunization program with questions about VFC and Abrysvo.

Last reviewed: August 24, 2025

All three RSV vaccines (Arexvy, Abrysvo, mResvia) are administered by the intramuscular route.

Last reviewed: August 24, 2025

Yes. It is acceptable to administer any of the three available RSV vaccines at the same time as other recommended vaccines, in accordance with CDC’s general best practice guidelines for immunization. This is especially important if you are concerned an unvaccinated patient will not return or if the patient’s immediate risk is high (such as when seasonal influenza, RSV, and COVID-19 are circulating).

Coadministration might increase short-term side effects (greater reactogenicity), such as fever, soreness, body aches, or headache, especially when administering more than one vaccine containing a non-aluminum adjuvant designed to enhance the immune response. While these side effects are not unsafe, they may be unpleasant for a day or two. If you are confident that a patient will return, the patient may prefer to separate the administration of vaccines that are less time-sensitive (e.g., shingles vaccine) to reduce the likelihood of uncomfortable side effects. There is no specific minimum interval between non-live vaccines, so separation by just a few days is acceptable, if desired.

Last reviewed: August 24, 2025

The safety and effectiveness of RSV vaccines have not been studied in infants. The family should be informed of the error, and an RSV preventive antibody product, either nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck), should be administered as recommended as soon as feasible. CDC experts recommend that if you administer the preventive antibody product within 72 hours of the error, and you know where the RSV vaccine was injected, you should administer the preventive antibody product in a different anatomic site. Facilities that stock RSV vaccine and RSV preventive antibody products should put systems and procedures in place to prevent this type of error, including staff training, clear labeling, and warnings in storage units. This medication error and any suspected adverse events following the error should be reported to the Vaccine Adverse Event Reporting System (VAERS) at  https://vaers.hhs.gov.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Vaccination involves active immunization, where an antigen is administered to a recipient to activate the recipient’s immune system and generate an immune response (which includes developing antibodies). Active immunization may require up to 2 weeks to have its full protective effect, and sometimes a series of vaccinations is required. Protection may last for months or be life-long, depending upon the type of immune response triggered. The effectiveness of a vaccine depends on the recipient’s immune system.

Nirsevimab (Beyfortus, Sanofi) and clesrovimab (Enflonsia, Merck) are injectable, long-acting monoclonal antibody products that gives the recipient direct, immediate protection through passive immunization. The antibodies circulate in the bloodstream and recognize and attach to the RSV virus if encountered, leading to elimination of the virus. These antibodies protect the patient for at least 5 months until they gradually break down and disappear. The highest risk of severe RSV infection and hospitalization for children is during their first RSV season as an infant. RSV preventive antibody products will not prevent children from getting RSV infections in future seasons, but the general risk of hospitalization due to RSV in childhood is far lower after infancy.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Clinical trials of nirsevimab (Beyfortus, Sanofi) in infants less than 8 months old born during or entering their first RSV season showed that giving nirsevimab reduced the risk of RSV-associated lower respiratory tract infection (LRTI) requiring a medical visit or hospitalization by approximately 80 percent and reduced the risk of ICU admission for this reason by 90 percent.

Clinical trials did not study hospitalization rates among older infants and toddlers at high risk of severe RSV disease in their second RSV season. Instead, a study was done to measure blood levels of nirsevimab given to infants and toddlers at increased risk for severe RSV disease (certain preterm infants and those with serious heart or lung disease). The blood levels of nirsevimab were equivalent to the levels in healthy infants in the clinical trial who received nirsevimab in their first RSV season. Based on this finding, it is estimated that their protection from serious infection would also be similar.

Last reviewed: August 24, 2025

Clesrovimab (Enflonsia, Merck) is a preventive antibody product approved in mid-2025 to be administered intramuscularly as a single 105 mg dose to infants from age 0 days to age 8 months and 0 days either before or during their first RSV season. It is recommended for use as an option for prevention of serious lower respiratory tract infection with RSV in infants. There is no preference between clesrovimab and nirsevimab (Beyfortus, Sanofi) for eligible infants. However, only nirsevimab is approved for high-risk children age 8 through 19 months entering their second RSV season.

Clinical trials demonstrated clesrovimab had benefits similar to nirsevimab, with a 60% reduced risk of medically attended lower-respiratory tract illness (MALRI) caused by RSV and an 84% reduced risk of hospitalization with RSV LRI during the 150 days after administration.

Last reviewed: August 24, 2025

The nirsevimab (Beyfortus, Sanofi) and clesrovimab (Enflonsia, Merck) clinical trials demonstrated effective protection lasted at least 5 months (150 days) in preventing severe RSV disease (disease requiring medical attention or hospitalization). Protection may persist longer than 5 months, but this was the period of time studied in the trials.

Last reviewed: August 24, 2025

Yes, they are. Infants and toddlers eligible for the VFC program may receive nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) when recommended, just as they would receive VFC vaccines. Providers who participate in VFC should follow all VFC requirements for ordering, storage, and administration established by their state immunization program.

Last reviewed: August 24, 2025

Palivizumab (Synagis) is a short-acting monoclonal antibody for the prevention of RSV disease in certain high-risk infants. It is given as a series of 5 monthly injections during an RSV season. With the availability of two long-acting preventive antibody products, clesrovimab and nirsevimab, each requiring only one dose for an entire RSV season, the American Academy of Pediatrics no longer recommends Synagis. The manufacturer has announced that the product is to be discontinued in December 2025.

Last reviewed: August 24, 2025

ACIP recommends one dose of either nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) preventive antibody for all infants less than 8 months and 0 days of age who are born during or are entering their first RSV season. Infants whose mothers received a dose of Abrysvo RSV vaccine as recommended during pregnancy are not recommended to receive an RSV preventive antibody product, except in special circumstances when protection from the vaccine is not considered adequately effective (see this question).

ACIP also recommends one dose of nirsevimab (Beyfortus) for specific young children age 8 through 19 months who are entering their second RSV season and at increased risk for severe RSV disease. These include the following:

Children 8 through 19 months at high risk:

  • Children with chronic lung disease of prematurity who require medical support during the six months before the start of their second RSV season
  • Children who are severely immunocompromised
  • Children with evidence of severe cystic fibrosis (previous hospitalization for pulmonary exacerbation in the first year of life or abnormalities on chest imaging that persist when stable) or that have weight-for-length that is less than the 10th percentile
  • American Indian or Alaska Native children entering their second RSV season. This is especially important for those who are in remote regions or in communities known to have increased rates of severe RSV disease in children.

The full ACIP recommendation for nirsevimab is available at www.cdc.gov/mmwr/volumes/72/wr/pdfs/mm7234a4-H.pdf.

The full ACIP recommendation for clesrovimab is available at www.cdc.gov/mmwr/volumes/74/wr/pdfs/mm7432a3-H.pdf.

Find further clinical considerations and information at CDC’s web page for healthcare providers on RSV immunization for infants and young children: www.cdc.gov/vaccines/vpd/rsv/hcp/child.html.

Last reviewed: August 24, 2025

Infants and children 8 months through 19 months of age who meet one or more of the criteria listed below are recommended to receive 200 mg of nirsevimab (Beyfortus, Sanofi), administered as two 100-mg manufacturer-filled syringe (MFS) injections given at the same time at different injection sites) just before or during their second RSV season:

  • Children with chronic lung disease of prematurity who required medical support (chronic corticosteroid therapy, diuretic therapy, or supplemental oxygen) any time during the 6-month period before the start of the second RSV season
  • Children with severe immunocompromise
  • Children with cystic fibrosis who have either 1) manifestations of severe lung disease (previous hospitalization for pulmonary exacerbation in the first year of life or abnormalities on chest imaging that persist when stable), or 2) weight-for-length less than the 10th percentile
  • American Indian or Alaska Native (AI/AN) children, particularly those who live in remote regions, where access to medical care may be challenging, or in areas where there are known high rates of severe disease among older infants and toddlers
Last reviewed: August 24, 2025

The answer is no. ACIP recommends only a single dose of RSV preventive antibody product for infants younger than 8 months of age, administered during, or just before, RSV season. An infant who receives nirsevimab at the end of one season and who is younger than age 8 months at the beginning of the next season should not be given an additional dose of either RSV preventive antibody product. Likewise, children younger than 8 months of age born near the end of the previous RSV season to mothers who received an effective dose of Abrysvo RSV vaccine during pregnancy are NOT recommended to receive an RSV preventive antibody product at the beginning of the next season.

Children who meet the high-risk criteria to receive a dose of nirsevimab to protect them through their second RSV season should be at least 8 months of age (and younger than 20 months of age) at the time of administration of the second-season nirsevimab dose.

Last reviewed: August 24, 2025

The optimal timing for nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) to be administered is shortly before the RSV season begins; however, these products may be administered to eligible infants and children at any time during the season.

The time to administer RSV preventive antibody products is during the months of October through March in most areas in the United States, unless otherwise advised by state or territorial public health authorities. Adjustment of timing due to RSV activity outside this typical timeframe is most likely to be necessary in tropical or sub-tropical climates and in Alaska.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Some American Indian or Alaska Native (AI/AN) children experience higher rates of severe RSV disease than the general population. A recent study found that the incidence of hospitalization due to RSV among some AI/AN children in their second year of life was four to ten times higher than that of similar-aged children in multiple study sites in the United States. Also, some AI/AN communities live in remote regions, making transportation of children with severe RSV to obtain medical care more challenging. Although the available data are limited and may not apply to all AI/AN children in all settings, ACIP recommends nirsevimab (Beyfortus, Sanofi) for AI/AN children entering their second RSV season.

The American Academy of Pediatrics (AAP) explains its recommendation for AI/AN children in its August 2025 policy statement (https://doi.org/10.1542/peds.2025-073923) as follows:

American Indian and Alaska Native Children are included in the high-risk category, because they experience significantly higher rates of severe RSV disease and hospitalization, with children living in rural and reservation communities most impacted. Evidence supports that this increased risk is associated with social drivers of health, with specific attention to running water access, transportation difficulties, household crowding, and indoor air quality.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Palivizumab (Synagis, AstraZeneca) is a short-acting monoclonal antibody product that is administered monthly. Synagis is no longer recommended for use by the American Academy of Pediatrics (AAP). The manufacturer is discontinuing the product in December 2025.

Last reviewed: August 24, 2025

If you are unable to obtain prenatal records or verify receipt of maternal RSV vaccine, CDC recommends that the baby receive nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck), particularly if it is shortly before or during the RSV season. Don’t forget to check the state immunization information system (IIS) for the mother’s vaccination record. RSV vaccination during a previous pregnancy does not protect through later pregnancies. If the mother received RSV vaccine during a previous pregnancy, nirsevimab or clesrovimab is indicated for this infant. It is also important to attempt to verify from the birthing facility records whether this baby received an RSV preventive antibody product prior to discharge to avoid giving an unnecessary second dose.

Last reviewed: August 24, 2025

Yes. Infants born less than 14 days after the mother received RSV vaccine should receive nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck). Infants born within 14 days after maternal vaccination may not have had sufficient time in utero to receive adequate protection from maternal RSV antibodies produced after vaccination. Infants born 14 days or more after maternal vaccination are not recommended to receive an RSV preventive antibody product except in rare circumstances where maternal antibodies may be insufficiently effective. See a separate question for details on those circumstances.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

In rare circumstances, nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) may be considered for infants in their first RSV season who were born to RSV-vaccinated mothers. These situations may include:

  • infants born to mothers who have health conditions that might prevent an adequate maternal immune response to vaccination (an immunocompromising condition caused by disease or immunosuppressive treatment)
  • infants whose mothers have conditions associated with reduced transplacental antibody transfer (such as a mother living with HIV infection)
  • infants who might have lost maternal antibodies, such as those who have undergone cardiopulmonary bypass or extracorporeal membrane oxygenation (ECMO)
  • infants with substantially increased risk for severe RSV disease (such as hemodynamically significant congenital heart disease or intensive care admission requiring oxygen at hospital discharge).

Infants and children age 8 through 19 months who are at increased risk for severe RSV disease and are entering their second RSV season are recommended to receive nirsevimab (Beyfortus) regardless of history of maternal vaccination. Clesrovimab is not recommended for children age 8 months or older.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

ACIP routinely recommends nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) only for infants younger than 8 months of age whose mothers were not vaccinated, or not effectively vaccinated, with Abrysvo (Pfizer) RSV vaccine during their pregnancy. RSV preventive antibody products are not recommended for this infant unless there is a clinical reason to believe maternal vaccination was ineffective, for example, if the infant had been born less than 14 days after vaccine administration. See this question for additional information about when to consider an RSV preventive antibody product for the infant of a vaccinated mother.

Last reviewed: August 24, 2025


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Last reviewed: August 24, 2025

Nirsevimab (Beyfortus, Sanofi) dosing is based upon weight and/or age. It is available in 50-mg or 100-mg manufacturer-filled syringes (MFS). Infants younger than 8 months and weighing less than 5 kgs (11 lbs.) should receive a 50-mg dose, given as a 50-mg MFS. Infants younger than 8 months and weighing 5 kg (11 lb.), or more, should receive a single 100-mg dose, given as a 100-mg MFS. Infants and toddlers age 8 months through 19 months who need nirsevimab should receive a 200-mg dose, given as two 100-mg MFS.

Avoid administering two 50-mg MFS to an infant who needs a 100-mg MFS. The 50-mg MFS is intended for the smallest infants. The cost of the 50-mg and 100-mg MFS are equivalent, despite the difference in dose; insurance plans may not cover the cost of two doses given to an infant not recommended to receive two doses. Only high-risk children age 8 through 19 months are recommended to receive two (100-mg) MFS doses at the same visit.

See the Immunize.org standing order template for details: www.immunize.org/wp-content/uploads/catg.d/p3097.pdf.

Last reviewed: August 24, 2025

The 50-mg manufacturer-filled syringes (MFS) of nirsevimab (Beyfortus) should be reserved for infants weighing less than 5 kilograms (less than 11 pounds). The cost of a single MFS is the same, whether it is a 50-mg MFS or a 100-mg MFS. Insurers are likely to cover only the cost of one MFS dose to an infant younger than age 8 months. Only high-risk children age 8 through 19 months are recommended to receive two (100-mg) MFS doses at the same visit.

Last reviewed: August 24, 2025

This question has arisen more frequently since the introduction of the RSV preventive antibody, nirsevimab (Beyfortus, Sanofi), which has an injection volume of 1 mL for infants younger than age 8 months who weigh 5 kg or more at the time of immunization. High-risk children entering their second RSV season require a Beyfortus dose volume of 2 mL. Beyfortus is often administered at a routine visit when other infant immunizations are due.

There is no specific guidance to not exceed 1 mL in one muscle. In fact, there is no clear standard of practice and reference texts vary in guidance. Facilities or health systems may have medication policies/procedures that outline guidance for their staff. Professional judgement is needed when administering intramuscular medications or immunizations to people, including children, because muscle size varies from person to person.

CDC experts suggest a range of volume, depending upon the muscle injected. For the deltoid, the typical volume injected is 0.5 mL (maximum: 2 mL). For the vastus lateralis (the thigh): the typical volume that may be injected is 1–4 mL (maximum: 5 mL). Infants and toddlers fall at the lower end of these ranges, whereas adolescents and adults generally fall on the higher end of the range.

If more than 1 mL of volume needs to be injected into the thigh, that can be done while staying well within the acceptable range. Use of combination vaccines, when indicated and available, can decrease injection volume.

Last reviewed: August 24, 2025

Yes, nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) may be coadministered with all other recommended age-appropriate vaccines. An RSV preventive antibody product should not interfere with the immune response to routine childhood vaccines when given together or at any time before or after them. Likewise, vaccination does not interfere with the effectiveness of the preventive antibody product.

When giving several injections at a single visit, separate intramuscular vaccines by at least 1 inch in the body of the muscle, if possible, to reduce the likelihood of overlapping local injection site reactions.

Last reviewed: August 24, 2025

No, these two antibody preparations should not interfere with each other. Administer nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) as recommended.

Last reviewed: August 24, 2025

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