Beyfortus (nirsevimab-alip) is a prescription drug that’s used to prevent severe illness caused by respiratory syncytial virus (RSV) infection. The drug comes as a liquid solution in a syringe for injection into a muscle.

Beyfortus is used in certain children to prevent severe illness caused by RSV infection.

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

Beyfortus belongs to a group of drugs called monoclonal antibodies. This article describes the dosages of Beyfortus, as well as its strengths and how it’s given. To learn more about Beyfortus, see this in-depth article.

* 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.

This section describes the usual dosages of Beyfortus. Keep reading to learn more.

What is Beyfortus’s form?

Beyfortus is available as a liquid solution. It comes in a prefilled syringe for single use. Beyfortus is injected into a muscle by a healthcare professional.

What strengths does Beyfortus come in?

Beyfortus comes in two strengths:

  • 50 milligrams (mg) per 0.5 milliliter (mL)
  • 100 mg per 1 mL

What are the usual dosages of Beyfortus?

Your child’s doctor will give the recommended dosage of Beyfortus based on your child’s age, body weight, and risk for respiratory syncytial virus (RSV) infection.

The information below describes dosages that are commonly used or recommended. Your child’s doctor will determine the best dosage that fits their needs.

What’s the dosage of Beyfortus for children?

Beyfortus is used to help prevent severe illness caused by RSV infection in children up to 2 years of age.

The dosage for newborns and infants up to 1 year of age, born during or entering their first RSV season, is:

  • 50 mg for babies who weigh less than 5 kilograms (kg)*
  • 100 mg for babies who weigh 5 kg or more

For children younger than 24 months who are still at risk for RSV infection in their second RSV season, the dosage is 200 mg (two 100-mg injections).

For more information about Beyfortus’s dosage for children, talk with your child’s doctor or a pharmacist.

* One kg equals about 2.2 pounds (lb).

Is Beyfortus used long term?

No. Beyfortus is typically given as a one-time injection during a child’s first RSV season. In some cases, your child’s doctor may recommend a second injection to prevent infection during the child’s second RSV season.

Dosage adjustments

Your child’s doctor may recommend an extra dose of Beyfortus in some cases. Children undergoing certain types of heart surgery may need an extra dose of Beyfortus to lower their risk for RSV infection. The extra dose of Beyfortus would be given as soon as they’re stable after heart surgery.

The dosage of Beyfortus prescribed for your child may depend on several factors. These include:

  • your child’s age
  • your child’s body weight
  • your child’s overall health
  • other conditions they may have (see the “Dosage adjustments” section above)

Beyfortus is available as a liquid solution in a prefilled syringe. It’s given as an injection into the muscle of the thigh by a healthcare professional. Your child will receive Beyfortus at their doctor’s office.

Below are answers to some commonly asked questions about Beyfortus’s dosage.

How long does it take for Beyfortus to start working?

Beyfortus starts to work soon after your child receives their dose. Because of how the drug works, they likely won’t feel the drug working.

If you have other questions about what to expect from Beyfortus preventive treatment, talk with your child’s doctor.

Can Beyfortus be used for the flu? If so, what’s the dosage?

No, Beyfortus is not used for the flu. Although respiratory syncytial virus (RSV) infection has some symptoms that are similar to flu symptoms, the two infections are caused by different viruses.

Beyfortus is a monoclonal antibody. It works like the antibodies your child’s body makes to fight the virus that causes RSV infection. Beyfortus helps prevent severe illness caused by RSV infection.

If you’re interested in learning more about flu treatments, talk with your doctor.

The sections above describe the usual dosages provided by the manufacturer. If your child’s doctor recommends Beyfortus for your child, they’ll prescribe the dosage that’s right for your child.

Talk with your child’s doctor if you have questions or concerns about their dosage.

Here are some examples of questions you may want to ask your child’s doctor:

  • Can my child receive Beyfortus if they’re older than 24 months?
  • Will my child need more than two doses of Beyfortus?
  • Does my child’s Beyfortus dosage depend on whether they have a lung condition?

To get information on different conditions and tips for improving your health, subscribe to any of Healthline’s newsletters. You may also want to check out the online communities at Bezzy. It’s a place where people with certain conditions can find support and connect with others.

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.