Beyfortus (nirsevimab-alip) is a brand-name injection that’s prescribed to prevent serious illness caused by respiratory syncytial virus (RSV) in certain children. As with other drugs, Beyfortus can cause side effects, such as injection site reactions.

Beyfortus can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, are bothersome, or become severe, be sure to talk with your child’s doctor or pharmacist.

These are just a few of the more common side effects that were reported after receiving Beyfortus in clinical trials:

  • skin rash
  • injection site reaction

For more information about these side effects, see “Side effect specifics” below.

Mild side effects can occur with Beyfortus. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Beyfortus’s prescribing information.

Mild side effects that have been reported with Beyfortus include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, are bothersome, or become severe, be sure to talk with your child’s doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If your child develops a side effect after receiving Beyfortus and you want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics” below.
† An allergic reaction is possible after receiving Beyfortus. However, it’s not clear whether this side effect occurred in clinical trials. To learn more, see the “Side effect specifics” section below.

Serious side effects from Beyfortus were rare in clinical trials, but they can occur. For more information, you can refer to Beyfortus’s prescribing information.

If your child develop serious side effects after receiving Beyfortus, call your doctor right away. If the side effects seem life threatening or you think they’re having a medical emergency, immediately call 911 or your local emergency number.

Beyfortus can cause serious side effects, including a severe allergic reaction. However, it’s not clear whether this side effect was reported in clinical trials. To learn more, see the “Side effect specifics” section.

Beyfortus may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

How do the side effects of Beyfortus compare with the side effects of Synagis?

Beyfortus and Synagis (palivizumab) are both injections that may be given to help prevent serious illness from RSV. For this reason, some of their side effects may be similar, and others may be different.

For example, Beyfortus and Synagis can both cause skin rash and injection site reactions.

However, Synagis may also cause a fever. This side effect was not reported in clinical trials of Beyfortus.

Talk with your child’s doctor to learn more about how Beyfortus and Synagis compare.

Does Beyfortus cause long-term side effects?

It’s not likely. No long-term side effects have been reported in clinical trials of the drug.

If you have concerns about long-term side effects from Beyfortus, talk with your child’s doctor.

Learn more about some of the side effects that Beyfortus may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for Beyfortus.

Skin rash

Beyfortus may cause a skin rash. In the drug’s clinical trials, this was the most frequently reported side effect. However, it wasn’t a common occurrence overall.

A skin rash can appear up to 14 days after your child receives their injection. Symptoms of a skin rash can include:

What you can do

If your child develops a rash after receiving a Beyfortus injection, talk with their doctor. Their doctor can help determine the cause of the rash and suggest ways to treat it.

Injection site reaction

Beyfortus is given as an intramuscular injection. As such, it’s possible for it to cause an injection site reaction. This was one of the most commonly reported side effects in Beyfortus’s clinical trials. However, it wasn’t commonly reported overall.

Injection site reactions can happen up to 7 days after the injection is given. Symptoms of an injection site reaction occur where the drug was injected. They may include:

  • pain
  • swelling
  • hardness under the skin

What you can do

Injection site reactions will typically go away on their own. If your child develops a reaction, you may be able to relieve some symptoms at home. For example, applying a cold compress to the area may help reduce pain and swelling.

Talk with your child’s doctor if you notice your child’s injection site reactions are getting worse over time instead of better.

Allergic reaction

As with most drugs, Beyfortus can cause an allergic reaction in some people. However, it’s not clear whether this side effect was reported in clinical trials of the drug.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under the skin, typically in your eyelids, lips, hands, or feet
  • swelling of the mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease any symptoms. However, if the symptoms are serious and you think your child may be having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your child’s doctor about their history before they receive Beyfortus. This drug may not be right option for your child if they have certain medical conditions or other factors that affect their health. These include:

Excessive bleeding: If your child has a bleeding condition, such as hemophilia or a low platelet count, talk with their doctor. These conditions can increase your child’s risk of bruising or bleeding after receiving Beyfortus. Other blood clotting disorders may also affect how quickly their body heals from this injection. Your child’s doctor will determine whether it’s safe for them to receive Beyfortus.

Medications prescribed to treat a blood clotting disorder: If your child is taking an anticoagulant drug, tell their doctor before they receive Beyfortus. This type of medication can limit how well their blood clots after receiving a Beyfortus injection. In turn, this may lead to a higher risk of bruising or bleeding. Your child’s doctor may recommend additional precautions before giving an injection of Beyfortus.

Allergic reaction: If your child has had an allergic reaction to Beyfortus or any of its ingredients, your child’s doctor will likely not prescribe Beyfortus. Ask them what other options may be better for your child.

Side effects after receiving Beyfortus aren’t common, but can happen. They are typically mild and go away on their own. If your child has side effects that are bothersome or become serious, talk with their doctor.

If you’d like to learn more about Beyfortus, talk with your child’s doctor or pharmacist. They can help answer any questions you have about side effects of the drug.

Besides talking with your child’s doctor, you can do some research on your own. These articles might help:

Disclaimer: Medical News Today 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.