Nirsevimab Frequently Asked Questions

About Nirsevimab

Are nirsevimab and clesrovimab vaccines?

Nirsevimab and clesrovimab are monoclonal antibody products that are passive immunizations. While not technically “vaccines” in a traditional sense (active immunization), they are being used in a manner similar to routine childhood vaccines and may be referred to as vaccines by some entities. Nirsevimab and clesrovimab confer long-lasting protection from RSV, with protection expected to last at least 5 months (about the length of a typical RSV season). Nirsevimab and clesrovimab are part of the Vaccines for Children program.

Because nirsevimab and clesrovimab are monoclonal antibody products, who can administer them?

Nirsevimab and clesrovimab come in prefilled syringes. In most states, anyone who can administer injections can administer nirsevimab and clesrovimab.

How effective is RSV immunization and how long does the RSV protection conferred by nirsevimab and clesrovimab last?

Protection from RSV immunization is expected to last at least 5 months, about the length of an RSV season, and is expected to reduce the risk of severe RSV disease by about 80%. Data from the 2024-2025 RSV season showed that nirsevimab was effective against RSV-associated emergency department encounters and hospitalization among infants in their first RSV season. Specifically, data from the VISION Multi-Site Network of Electronic Health Records of 160 emergency departments and 131 hospitals showed nirsevimab was 63% effective at preventing RSV-associated ED encounters and 79% effective at preventing RSV-associated hospitalization. 

Nirsevimab Ordering and Supply

Should we anticipate limitations in nirsevimab or clesrovimab supply for the 2025-2026 RSV season?

A shortage of nirsevimab and/or clesrovimab is not expected this coming season. Nirsevimab and clesrovimab are expected to be broadly available by October 1. Questions about ordering VFC doses should be directed to your state immunization program. Questions about private/commercial ordering should be directed to Sanofi at 855-BEYFORTUS for nirsevimab and to 877-VAX-MERCK for clesrovimab.

Given nirsevimab has a shelf life of about 18 months and clesrovimab has a shelf life of about 30 months, should I purchase extra doses to have on hand knowing I can always use them next season?

It is noted that data does not currently exist about the impact of temperature excursions on nirsevimab or clesrovimab; if temperature excursions occur, you will likely be advised to discard the product, which could have financial implications. Choices about quantities of product to purchase are individual, by practice or institution.

Can I administer two 50 mg doses of nirsevimab to my patient who is > 5 kg instead of a 100 mg dose?

Avoid using two 50 mg nirsevimab doses for infants weighing ≥5 kilograms (≥11 pounds), because 50 mg doses should be reserved for smaller infants who are at increased risk for severe RSV illness because of their smaller airways. Furthermore, providers should be aware that insurers may not cover the cost of two 50 mg nirsevimab doses for an individual infant.

Can we split a 100 mg manufacturer-filled syringe (MFS) of nirsevimab into two 50 mg doses?

No, nirsevimab 100 mg doses are approved for single use.  
 
Manufacturer-filled syringes are prepared with a single dose and sealed under sterile conditions by the manufactures. They do not contain a preservative to help prevent the growth of microorganisms.  
 
They are intended for ONE patient for ONE injection. Never administer medications from the same syringe to more than one patient, even if the needle is changed.  
 
Attempting to split 100 mg MFS into two 50 mg doses is a serious administration error that risks inadvertent contamination and infection transmission.

Palivizumab

If an infant received palivizumab in season 1, can they receive nirsevimab or clesrovimab?

If palivizumab was administered in season 1 and the child is eligible for RSV prophylaxis in season 2, the child should receive nirsevimab or clesrovimab in season 2.

Is palivizumab recommended?

No, palivizumab is no longer routinely recommended for use by the AAP and it will be discontinued as of December 31, 2025.

RSV Immunization Administration, Side Effects/Contraindications, and Timing

Can RSV immunization be co-administered with other routine vaccines?

Yes. In accordance with Immunize.org guidance, simultaneous administration of RSV immunization with age-appropriate vaccines is recommended. Nirsevimab and clesrovimab are not expected to interfere with the immune response to other vaccines and had similar safety and reactogenicity profiles to vaccines administered without nirsevimab or clesrovimab.

Are there maximum volumes of injectable vaccine, antibiotic or other products that can be administered into each muscle group for different ages? For example, at the 6-month well-child visit, could an infant receive RSV immunization, COVID-19, influenza, PCV, and DTaP-IPV-HepB-Hib?

In accordance with Red Book guidance, simultaneous administration of RSV immunization with age-appropriate vaccines is recommended.  CDC does not address the issue of maximum volumes that can be injected into each muscle group in different age groups. Based on discussions with CDC, AAP offers the suggested volumes as follows:

• Deltoid: Average 0.5 mL (range 0.5–2 mL)
• Vastus Lateralis: Average 1–4 mL (range 1–5 mL)

Infants and toddlers would fall at the lower end of the range, whereas adolescents and adults would generally fall on the higher end of the range. Strategies healthcare providers can use to decrease the number/injection volume include:

1. Healthcare providers should always use professional judgement when administering injections. Muscle size can vary greatly from one patient to another.
2. Include an age-appropriate combination vaccine in the facility’s inventory (Pentacel, Pediarix, Vaxelis).
3. Use an alternate route (other than IM) if possible.  IPV (single component, NOT a combination vaccine), MMR (toddlers and infant travelers only), Varicella-containing vaccines (toddlers only), and PPSV23 (high-risk toddlers only) can be administered subcutaneously.
4. Take advantage of recommended age ranges some of the routinely recommended vaccines have.  For example, the 3rd dose of HepB can be given as late as 18 months of age to children born to mothers who are HBsAg negative.

If a high-risk child mistakenly received a 100 mg dose of nirsevimab when they should have received a 200 mg dose, should we have them return for the other 100mg?

If a half dose is inadvertently given, another half dose should be administered as soon as possible, but no later than the end of the season (for most of the continental US, this would be through the end of March, unless local guidance is given to administer during a modified time period). This counts as a 200 mg dose.

What are the potential side effects of RSV immunization?

Immunize.org published an Immunization Information Statement (VIS-like document) for families. It states that “After getting an RSV preventive antibody, your child might have temporary pain, redness, swelling where the injection was given, or a rash.”  In addition, the nirsevimab package insert and clesrovimab package insert have additional information on adverse reactions. For nirsevimab, “Most common adverse reactions were rash (0.9%) and injection site reactions (0.3%).” For clesrovimab, “Most common adverse reactions were injection-site erythema (3.8%), injection-site swelling (2.7%), and rash (2.3%).

Are there any contraindications to receiving RSV immunization? Can an infant or young child receive RSV immunization when they are sick?

Both nirsevimab and clesrovimab are contraindicated in infants and young children with a history of serious hypersensitivity reactions, including anaphylaxis, to nirsevimab or clesrovimab or to any of their components. Illness or febrile diseases are not contraindications to receiving an RSV immunization. The AAP suggests following Immunize.org guidance, which recommends that vaccination should be deferred for persons with a moderate or severe acute illness, as this precaution avoids causing diagnostic confusion between the underlying illness and potential adverse effects of immunization. Similar to routine childhood vaccines, mild illness – with or without fever – should not be used as a reason to delay administration of nirsevimab or clesrovimab.  

What does "shortly before or during” the RSV season mean?  When should I start administering RSV immunizations?

In most of the continental US, “shortly before or during the season” means that administration of RSV immunizations should begin on October 1 and conclude on March 31. In tropical climates (southern Florida, Hawaii, Guam, Puerto Rico, US Virgin Islands and US-affiliated Pacific Islands) and Alaska, RSV circulation patterns may differ. Because timing of the onset, peak and decline of RSV activity may vary, providers can adjust administration schedules based on local RSV activity in the community.  The CDC monitors RSV activity in the United States in collaboration with state and county health departments and commercial and clinical laboratories. These data are available from the National Respiratory and Enteric Virus Surveillance System. Information about local epidemiology can be determined by contacting your local, state, tribal, or territorial health department or other local health authority. Optimal timing for RSV immunization administration is shortly before the RSV season begins, however, it may be given to eligible infants and toddlers who have not yet received a dose at any time during the season.

Per CDC, healthcare providers may choose to give nirsevimab or clesrovimab before the start of RSV season if they feel that the child may not return for a visit when RSV immunization would be recommended. For example, a clinician may choose to give RSV immunization to an infant who presented for care in September who has not yet received a dose of RSV immunization and may be unlikely to return for a visit in October or November. Nirsevimab and clesrovimab have been shown to protect against severe RSV disease for at least 5 months, and the ideal timing of administration may differ depending on the clinical situation.

How can pediatricians minimize the likelihood of immunization errors?

Vaccine providers who carry both infant RSV immunizations and RSV vaccine products for adults should be especially diligent in following vaccine administration safety procedures to prevent errors. To minimize risk of errors:

• Store nirsevimab/clesrovimab and RSV vaccine in their original packaging on different shelves and clearly label the shelves.
• Educate staff about the differences in indication including age for use, preparation, and dosage.
• Confirm with the patient or caregiver the product(s) they are expecting to receive.

RSV Immunization Recommendations

Are there changes to the recommendations for prevention of RSV in infants and young children for the 2025-2026 RSV season?

Recommendations have changed for the 2025-2026 RSV season to reflect that palivizumab is no longer routinely recommended for use and will be discontinued as of December 31, 2025 and that clesrovimab is recommended as an additional RSV immunization product available for infants in their first RSV season. All infants are recommended to be protected by either maternal RSV vaccination or RSV immunization administration for the 2025-2026 season.

Who is recommended to receive RSV immunization?

The American Academy of Pediatrics (AAP) recommends RSV immunization with nirsevimab or clesrovimab for:

• infants <8 months of age born during or entering their first RSV season if:
• pregnant parent did not receive RSVpreF vaccine during this pregnancy,
• pregnant parent’s RSVpreF vaccination status is unknown, or
• infant was born <14 days after the pregnant parent’s RSVpreF vaccination

The American Academy of Pediatrics (AAP) recommends RSV immunization with nirsevimab only for:

• infants and children 8 through 19 months of age at high risk of severe RSV disease and entering their second RSV season, regardless of the RSV vaccination status of the pregnant parent or the child’s prior receipt of nirsevimab or clesrovimab when <8 months of age. High-risk criteria include the following:
  • Children with chronic lung disease of prematurity who required medical support (chronic corticosteroid therapy, diuretic therapy, or supplemental oxygen) at 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:
    • 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
    • weight-for-length that is less than the 10th percentile
  • American Indian or Alaska Native children

Note that all ages refer to chronologic age, not corrected age.

Should a pregnant person receive maternal RSV vaccine during pregnancy this season if they received maternal RSV vaccine during pregnancy in a previous season?

No.  People who have received a maternal RSV vaccine during pregnancy should not receive additional doses during future pregnancies. Rather, that infant should receive nirsevimab or clesrovimab.  Additional data are needed to determine whether additional seasonal doses during subsequent pregnancies are indicated, and ACIP might update recommendations in the future, as data become available.

Should I administer RSV immunization to an infant who is born at the very end of the RSV season?

Yes. Optimal timing for administration is within 1 week after birth during the RSV season. Administering RSV immunization through the end of the season is important because the risk of severe disease is highest during the first few months of life and even when the season is over, RSV infections still occur, but at a lower incident rate.

If an infant’s gestational parent received RSV vaccine while pregnant with the infant, should the infant receive nirsevimab or clesrovimab?

The CDC does not recommend RSV immunization for most infants born to a mother who received maternal RSV vaccine during their most recent pregnancy, except for infants where less than 14 days have elapsed between vaccination and birth.  

RSV immunization can be considered for infants born to a mother who received maternal RSV vaccine when, per the clinical judgement of the healthcare provider, the potential incremental benefit of administration is warranted, including but not limited to the following rare circumstances:

• Infants born to pregnant people who may not mount an adequate immune response to vaccination or have conditions associated with reduced transplacental antibody transfer
• Infants who have undergone cardiopulmonary bypass or extracorporeal membrane oxygenation leading to loss of maternal antibodies
• Infants with substantial increased risk for severe RSV disease (eg, hemodynamically significant congenital heart disease, intensive care admission and requiring oxygen at discharge)

I have a healthy patient who was 7 months old in October. They present to the clinic in November, at 8 months of age. Can they receive RSV immunization at this visit?

No. CDC recommends that only those healthy infants younger than 8 months of age at the time of administration receive RSV immunization.

Can a baby who is 9 months old but corrects to 6.5 months due to prematurity (delivery at 29 weeks gestational age) receive RSV immunization?

In accordance with CDC General Best Practice Guidelines for Immunization preterm infants (infants born before 37 weeks’ gestation), regardless of birth weight, should receive RSV immunization at their chronological age using the same guidance for full-term infants and young children.  

Will infants born during the RSV season receive RSV immunization before they are discharged from the hospital?

It is recommended that infants born shortly before and during the RSV season receive RSV immunization within the first week of life, including in hospital settings. Infants with prolonged birth hospitalizations because of prematurity or other causes should receive RSV immunization shortly before or promptly after discharge. If a hospital has been unable to implement administration of nirsevimab or clesrovimab, the infant should receive RSV immunization in an ambulatory setting as soon as available. Currently, few hospitals participate in the VFC program, and additional advocacy to support hospital participation is ongoing. Timely and well-coordinated communication between birth hospital and the medical home is important. Equitable access to RSV immunization will require those in a community to work together.

Which children should receive a dose of nirsevimab in their second RSV season?

Infants and children 8 through 19 months of age who are at increased risk of severe RSV disease and entering their second RSV season, regardless of RSV vaccination status of the pregnant parent. This includes the following:

• Infants and children with chronic lung disease of prematurity who required medical support (chronic corticosteroid therapy, diuretic therapy, or supplemental oxygen) at any time during the 6-month period before the start of the second RSV season.
• Infants and children who are severely immunocompromised.
• Infants and children with cystic fibrosis who have 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 have weight-for-length that is less than the 10th percentile.
• American Indian and Alaska Native children.

If a patient was born towards the end of March and did not receive RSV immunization, can they receive RSV immunization in October?

Yes. Per AAP’s guidance, healthy infants born at the end of their first RSV season who did NOT receive RSV immunization (and whose birthing parent did not receive RSV vaccine during pregnancy) may receive one dose of RSV immunization if they are < 8 months of age entering their second RSV season.

If a standard risk patient was born last March and received RSV immunization and will be < 8 months of age in October, can they receive another dose of RSV immunization?

No. The infant is not eligible to receive RSV immunization since it is their second RSV season. Only children who meet high-risk criteria should receive more than one dose of RSV immunization. For more details on high-risk criteria, please see the full AAP recommendations here.

Why are infants 8-12 months old ineligible to receive RSV immunization (unless they are considered high-risk)?

The highest risk for severe RSV is in children under 6 months of age.  Infants 8 months and older will be entering their second RSV season and have likely already experienced their first RSV infection and will not receive the full benefits of RSV immunization.  

What is the guidance for high risk infants who are 19-24 months of age, particularly given nirsevimab has been FDA approved for infants and toddlers 24 months of age and younger who are at high risk for severe RSV illness?

A dose of nirsevimab is recommended for some children aged 8 through 19 months who are at increased risk for severe RSV and who are entering their second RSV season (note this is inclusive of 19 months). Nirsevimab provides at least 5 months of protection and should be offered to eligible children when entering the RSV season.

Nirsevimab is not recommended for any child who is age 20 months and older. Children ages 20 months and older have likely already experienced two RSV seasons and been infected with RSV, and thus are less likely to benefit from nirsevimab. Clesrovimab is not recommended for any child who is age 8 months and older.

Should an infant who had a confirmed RSV infection this season still receive RSV immunization?

Prior infection should generally not be used to determine an infant’s eligibility for RSV immunization.

What if a young infant is in our office and diagnosed with RSV that day or are within 48 hours of illness onset? Would a dose of RSV immunization be helpful to them to reduce the severity of the illness?

Nirsevimab and clesrovimab have not been studied as a treatment in infants with RSV and is not licensed for treatment of RSV disease. RSV immunization should be given prior to onset of the RSV season or as soon as possible after birth for infants born during the season to prevent severe RSV disease.

Coding and Payment

Is RSV immunization financially feasible for my practice? What flexibilities are available when I implement RSV immunization in my practice?

• There is no minimum order size. Nirsevimab is packaged as five single dose prefilled syringes per carton in both formulations. Clesrovimab is packaged as either one single dose prefilled syringe or ten single dose prefilled syringes. 
• Nirsevimab is fully returnable upon expiration. Sanofi offers credit (credit based on exact amount returned and the invoice purchase price that is net of prompt pay or other discount(s)) upon expiration on all full and open box Sanofi product(s) directly purchased from Sanofi that are returned within 1 year after the expiration date.

How do I code and bill for RSV immunization? Will I be paid appropriately?

See current coding and billing recommendations, including Coding Vignettes, on the nirsevimab Coding and Payment page.

Does RSV immunization require insurance prior authorization?  

In most instances, RSV immunization does not require insurance preauthorization. Please report any payer concerns or hassles to the Coding & Payment Hotline.

Reporting

If a patient has an adverse reaction to RSV immunization, where should it be reported?

Adverse events when giving an RSV immunization alone should be reported to the  FDA’s MedWatch Adverse Event Reporting Program.  

If an adverse event occurs while co-administering RSV immunization with a vaccine, it should be reported to the  Vaccine Adverse Event Reporting System. 

Do I need to report RSV immunization administration to my state immunization information system (IIS)?

Yes. You should report RSV immunization administration to the state IIS in accordance with state policies for reporting of vaccine administration.  

Talking to Families

Will there be a Vaccine Information Statement (VIS) available for RSV immunization?  

CDC has developed a “VIS-like” document – called an Immunization Information Sheet on RSV immunization. You are encouraged to share this document with parents/families when administering nirsevimab. You can download a copy on the CDC site.  

What resources are available for talking to families about RSV immunization?  

Please visit www.healthychildren.org/rsv for resources on talking about RSV immunization with families.  In addition, AAP has a patient brochure on RSV that is available in various languages. The AAP also offers Immunization Discussion Guides. They include talking points for clinicians and family-friendly infographics about recommended immunizations that care be shared during patient encounters or outside the clinical visit. RSV speaking points and RSV infographics  are also available.

How can families prevent RSV infection?  

Families should take preventative measures to stop the spread of RSV and other respiratory illnesses, including washing hands, covering coughs and sneezes, cleaning frequently touched surfaces, and staying home when sick. 

Expectant parents should talk with their healthcare provider about receiving the RSV vaccine (Abrysvo, Pfizer) during pregnancy to protect their infant from severe RSV. AAP recommends that all infants are protected against RSV through either vaccination of the mother with RSV vaccine during pregnancy or giving the infant RSV immunization after birth.

Parents should talk with their healthcare provider about whether RSV immunization is available for their infant.