Beyfortus (nirsevimab-alip) is a prescription drug that’s used to help prevent serious illness from respiratory syncytial virus (RSV) in certain children. Beyfortus comes as a solution that’s injected into the muscle.

Beyfortus basics

Beyfortus contains the active ingredient nirsevimab-alip.* (An active ingredient is what makes a drug work.)

Beyfortus is a brand-name drug. It’s not currently available in a generic form.

* The reason “-alip” appears at the end of the drug’s name is to show that the drug is distinct from similar medications that may be created in the future.

Whether you have health insurance or not, cost may be a factor when you’re considering Beyfortus. What you’ll pay for the drug may depend on other factors as well. Talk with your child’s doctor or your insurance provider (if you have one) to learn more about what you’ll pay for Beyfortus.

You can check out this article to learn more about saving money on prescriptions.

Other drugs are available that can prevent illness from respiratory syncytial virus. If you’d like to explore an alternative to Beyfortus, talk with your child’s doctor.

Palivizumab (Synagis) is a drug that’s similar to Beyfortus. For more information about the best option for your child, talk with their doctor.

Your child’s doctor will recommend the Beyfortus dosage that’s right for them. Below are commonly used dosages, but the dosage your child receives will be determined by their doctor.

Form and strengths

Beyfortus is available as a liquid solution that’s given as an injection into the muscle. It comes in two strengths:

  • 50 milligrams (mg) in 0.5 milliliters (mL) of solution
  • 100 mg in 1 mL of solution

Recommended dosages

To help prevent serious illness from respiratory syncytial virus (RSV), your child will get one dose of Beyfortus in their first RSV season (from fall to spring).

Your child’s doctor may recommend a second dose of Beyfortus if your child is younger than 2 years and has a higher risk of developing RSV. Children with a high risk of RSV-related illness after their first birthday include those with:

  • a weakened immune system
  • long-term heart or lung disease
  • a neuromuscular disorder such as muscular dystrophy

In addition, children ages 24 months and younger who have heart surgery with bypass* may need a second dose of Beyfortus after surgery.

If you have questions about the dosage of Beyfortus your child needs, talk with their doctor. And to learn more about the dosages of Beyfortus, see this article.

* With bypass surgery, a machine temporarily takes over the function of the heart and lungs during the procedure.

How it’s given

Your child’s doctor will explain how Beyfortus will be administered. They’ll also determine whether your child may need an additional dose.

Beyfortus comes as a liquid solution that’s given as an injection into the muscle, usually into the thigh. Your child will receive their Beyfortus dose at their doctor’s office.

If you have other questions about how your child’s dose of Beyfortus will be given, talk with their doctor.

Like most drugs, Beyfortus may cause mild or serious side effects. The lists below describe some of the more common side effects that Beyfortus may cause. These lists don’t include all possible side effects.

Keep in mind that side effects of a drug can depend on:

  • age
  • other health conditions your child has
  • other medications your child takes

Your child’s doctor can tell you more about the potential side effects of Beyfortus. They can also suggest ways to help reduce side effects.

Mild side effects

Here’s a list of some of the mild side effects that Beyfortus can cause. To learn about other mild side effects, talk with your child’s doctor or read Beyfortus’s prescribing information.

Mild side effects of Beyfortus that have been reported include:

Mild side effects of many drugs may go away within a few days to a couple of weeks. But if they become bothersome, talk with your child’s doctor.

* To learn more about this side effect, see the “Allergic reaction” section below.

Serious side effects

Serious side effects from Beyfortus can occur, but they aren’t common. If your child has serious side effects from Beyfortus, call their doctor right away. But if you think you’re child is having a medical emergency, you should call 911 or your local emergency number.

Serious side effects that can occur with Beyfortus include severe allergic reaction. To learn more about this side effect, see the “Allergic reaction” section below.

Allergic reaction

Some children may have an allergic reaction to Beyfortus. Symptoms of a mild allergic reaction can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)

A more severe allergic reaction is rare but possible. Symptoms of a severe allergic reaction can include swelling under the skin, usually in the eyelids, lips, hands, or feet. They can also include swelling of the tongue, mouth, or throat, which can cause trouble breathing.

Call your child’s doctor right away if they have an allergic reaction to Beyfortus. But if you think they’re having a medical emergency, call 911 or your local emergency number.

Beyfortus is used to prevent serious illness from respiratory syncytial virus (RSV) in:

  • babies younger than 1 year who were born during or are entering their first RSV season (fall to spring)
  • children up to age 24 months who have a high risk of serious illness from RSV through their second RSV season

Children with a high risk of RSV-related illness after their first birthday include those with:

  • a weakened immune system
  • long-term heart or lung disease
  • a neuromuscular disorder such as muscular dystrophy

In addition, children ages 24 months and younger who have heart surgery with bypass* may need a second dose of Beyfortus after surgery.

RSV is a common respiratory virus that can affect adults and children. But in babies, RSV can be serious. It may cause symptoms such as fever, congestion, difficulty breathing, cough, or runny nose.

Beyfortus works to prevent serious illness from RSV by helping your child’s immune system attack the virus. If you have additional questions about how Beyfortus works, talk with your child’s doctor.

* With bypass surgery, a machine temporarily takes over the function of the heart and lungs during the procedure.

Below is important information you should consider before your child receives Beyfortus.

Interactions

Combining a drug with certain medications, vaccines, foods, and other things can affect how the drug works. These effects are called interactions.

Beyfortus is not known to interact with other medications, herbs, supplements, foods, or alcohol. The manufacturer of Beyfortus didn’t look at interactions in studies of the drug.

Before your child receives Beyfortus, talk with their doctor. Tell them about all prescription, over-the-counter, and other drugs your child takes. Also, tell them about any vitamins, herbs, and supplements your child takes. Sharing this information can help your child avoid potential interactions.

If you have questions about drug interactions that may affect your child, talk with their doctor or a pharmacist.

Warnings

Beyfortus can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Beyfortus is a good option for your child.

Talk with your child’s doctor about their health history before they receive Beyfortus. Be sure to tell them if any of the following factors apply to your child:

Find answers to some commonly asked questions about Beyfortus.

How does Beyfortus compare with Synagis?

Beyfortus and (palivizumab) Synagis are both used to prevent serious illness from respiratory syncytial virus (RSV) in certain children.

The drugs both come as liquid solutions that are injected into the muscle.

Beyfortus and Synagis belong to the same group of drugs, but they contain different active ingredients. (An active ingredient is what makes a drug work.) Beyfortus contains the active ingredient nirsevimab-alip,* and Synagis contains palivizumab.

If you have other questions about how Beyfortus and Synagis compare, talk with your child’s doctor. They can recommend the best medication for your child.

* The reason “-alip” appears at the end of the drug’s name is to show that it’s distinct from similar medications that may be created in the future.

Does Beyfortus cause long-term side effects?

It’s unlikely. Long-term side effects weren’t reported in studies of Beyfortus.

If you’re concerned about possible long-term side effects from Beyfortus, talk with your child’s doctor.

If you still have questions about Beyfortus, talk with your child’s doctor. Questions you may want to ask include:

  • How can I help prevent side effects that my child may experience from a Beyfortus injection?
  • How will you determine whether my child needs a second dose of Beyfortus?
  • Do any of my child’s other medications interact with Beyfortus?

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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.