Beyfortus (nirsevimab-alip) is a long-acting monoclonal antibody with activity against the respiratory syncytial virus (RSV) that may be used to protect neonates and infants against lower respiratory tract disease (LRTD) caused by RSV.

It may be used to protect neonates and infants born during or entering their first RSV season against RSV-caused lower respiratory tract infections and those infants who remain vulnerable through their second RSV season, such as those with congenital heart disease or chronic lung disease.

Beyfortus works by attaching to a protein on the surface of RSV called the F protein. When it attaches to this protein, it prevents the virus from entering cells, especially those in the lungs, by inhibiting the essential membrane fusion step in the viral entry process, neutralizing the virus, and blocking cell-to-cell fusion. Beyfortus is produced by recombinant DNA technology and is a human immunoglobulin G1 kappa (IgG1κ) monoclonal antibody. Triple amino acid substitution in the Fc region has increased its half-life which increases the length of time it stays effective.

Beyfortus was approved FDA-approved on July 17, 2023.

Serious hypersensitivity reactions, including anaphylaxis, have been reported with human IgG1 monoclonal antibodies.

Beyfortus is contraindicated in infants and children with a history of serious hypersensitivity reactions, including anaphylaxis, to nirsevimab-alip or to any of the other ingredients in Beyfortus.

The is no information regarding the administration of Beyfortus with other immunoglobulin products. Do not administer palivizumab to infants who have already received Beyfortus in the same season. Beyfortus may be administered to children who have received palivizumab in their first RSV season but remain vulnerable in their second season.

Use with caution in infants and children with thrombocytopenia, any coagulation disorder, or to individuals on anticoagulation therapy.

The safety and effectiveness of Beyfortus have not been established in adults or children older than 24 months of age.

Beyfortus is given by intramuscular injection, preferably into the anterolateral aspect of the thigh (the top, outer part of the thigh) by a healthcare professional. The gluteal muscle is not routinely used as an injection site because of the risk of damage to the sciatic nerve.

For infants born outside the RSV season, administer Beyfortus once before the start of the RSV season considering that the duration of protection provided by Beyfortus is approximately 5 months.

Beyfortus can be administered at the same time as childhood vaccines, at a different injection site. Do not mix Beyfortus with any vaccines or medications in the same syringe or vial.

Neonates and infants born during or entering their first RSV season

Administer starting from birth.

• Weight less than < 11lb (<5kg): 50mg given IM using a 0.5mL prefilled syringe.
• Weight ≥ 11lb (≥5kg): 100mg given IM using a 1mL prefilled syringe.

There is limited data available for the use of Beyfortus in extremely preterm infants (gestational age <29 weeks, who are less than 8 weeks of age.

Vulnerable children who remain at increased risk for severe RSV disease: Second RSV season

For children up to 24 months of age who remain at increased risk for severe RSV disease in their second RSV season:

• Administer a single 200mg dose as two IM injections (2 x 100 mg).

Infants undergoing cardiac surgery with cardiopulmonary bypass

For infants undergoing cardiac surgery with cardiopulmonary bypass, an additional dose may be administered once the infant is stabilized after surgery, depending on the length of time passed, and the number of RSV seasons the infant has been exposed to.

First RSV season:

• < 90 days of the first dose, administer 50mg or 100mg depending on body weight
• ≥ 90 days after the first dose, administer a single dose of 50mg regardless of body weight.

Second RSV season:

• < 90 days of the first dose, administer 200mg regardless of body weight
• ≥ 90 days since the first dose, administer 100mg regardless of body weight.

Get emergency medical help if your child develops signs of an allergic reaction to Beyfortus: symptoms include hives; difficulty breathing; swelling of the face, lips, tongue, or throat.

Beyfortus is generally well tolerated, and the most common side effects reported include a mild-to-moderate rash (occurring in 0.7% of infants) occurring within 14 days post-dose.

Other side effects that occurred in 0.3% to 0.5% of infants within 7 days postdose include fever and non-serious injection site reactions.

Beyfortus does not interfere with reverse transcriptase polymerase chain reaction (RT-PCR) or rapid antigen detection RSV diagnostic assays that employ commercially available antibodies targeting antigenic site I, II, or IV on the RSV fusion (F) protein.

For immunological assay results which are negative when clinical observations are consistent with RSV infection, it is recommended to confirm using an RT-PCR-based assay.

This list is not complete. Other drugs may interact with Beyfortus, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.