How Does Beyfortus Work? Plus, 6 Other Beyfortus FAQs Answered

Every fall, we prepare for the respiratory virus season, which includes influenza (the flu), COVID-19, and respiratory syncytial virus (RSV). Along with annual flu and COVID vaccines, RSV vaccines are also available for older adults and pregnant women. But for babies and certain young children, there’s another option to prevent RSV: Beyfortus (nirsevimab-alip).

Beyfortus offers protection, but it’s not classified as a traditional vaccine. How exactly does Beyfortus work? How quickly does it take effect? How long does its protection last? We answer these questions and more below.

1. How does Beyfortus work?

Beyfortus is an injectable monoclonal antibody medication that contains RSV antibodies. Antibodies are proteins made by your immune system that can quickly identify and fight off infections. But in this case, the antibodies in Beyfortus are made in a lab.

The antibodies in Beyfortus are engineered to bind to a specific protein found on RSV (called the pre-F protein). By binding to this protein, Beyfortus prevents RSV from entering and infecting cells in the body. It’s still possible to get RSV after Beyfortus, but it’s less likely to develop serious illness from the infection.

Beyfortus is given as 1 dose per RSV season. It’s injected into the thigh muscle by a healthcare professional.

2. Is Beyfortus a vaccine?

Technically, Beyfortus is not a vaccine. Beyfortus and vaccines both provide immunity, but they do this in different ways.

Vaccines provide active immunity by stimulating your immune system to produce protective antibodies. But Beyfortus provides passive immunity by giving RSV-fighting antibodies directly to your child.

Good to know: Abrysvo is an RSV vaccine that’s given during pregnancy to protect newborns against RSV for a period of time after birth. Abrysvo is a vaccine, but it also provides babies with passive immunity against RSV. This is because antibodies created by the mother’s immune system in response to the vaccine pass to the fetus.

3. Can Beyfortus be given with other vaccines?

Yes, Beyfortus can be given at the same time as other vaccines, including childhood vaccines. Although the data is limited, Beyfortus isn’t known to affect how well other vaccines work.

Talk to your child’s pediatrician to find out if your child is caught up with their vaccinations. If the timing lines up, they may suggest scheduling Beyfortus and certain routine vaccines during the same visit.

4. How long does Beyfortus take to work?

Beyfortus works faster than vaccines. This is because your body doesn’t need to make its own antibodies. It’s expected to start working within hours after the injection is administered. In studies, Beyfortus reached maximum levels in the bloodstream by day 6 after a dose was given.

EXPERT PICKS: WHAT TO READ NEXT

• About RSV: Respiratory syncytial virus (RSV) usually causes mild cold symptoms. But babies and older adults are more likely to develop severe illness. Here’s everything you need to know about RSV.

• Can RSV turn into pneumonia? Learn more about who’s at risk for developing pneumonia from RSV, symptoms to look for, and ways to stop it from happening.

• RSV vaccines: Learn more about the state of RSV vaccines, including what’s available and what’s being studied.

5. How effective is Beyfortus?

Babies and certain young children are particularly vulnerable to severe illness from RSV, including pneumonia and bronchiolitis (inflammation of the tiny airways in the lungs). One dose of Beyfortus is very effective at preventing severe RSV disease in these age groups.

Pooled evidence from clinical trials has shown that Beyfortus is about 80% effective at preventing RSV-related illness requiring a healthcare visit, including hospitalization, in babies under 8 months old. It was also found to be 90% effective at preventing intensive care unit visits in this age group.

Keep in mind that even if your child receives Beyfortus, it’s still possible for them to get RSV. But they’ll be less likely to develop serious illness or require hospitalization.

6. How long does protection from Beyfortus last?

Beyfortus is typically given during October through March. Protection lasts for at least 5 months. This should cover an entire RSV season.

The CDC recommends that children get a dose of Beyfortus within 1 week of birth if they’re born during October through March. Babies born outside RSV season (April through September) should ideally receive a dose in October or November. This is also the case for children 8 to 19 months old entering their second RSV season who are at an increased risk of severe RSV.

Keep in mind that the typical RSV season timing can be different in certain regions. Check with your child’s pediatrician to find out if and when your child should receive Beyfortus.

7. Is Beyfortus safe?

Yes, Beyfortus is considered safe when it’s used as recommended. But like most medications, it has some potential side effects to know about.

The most common side effect reported during Beyfortus studies was a rash. This typically occurred within 2 weeks of getting the injection. Injection site reactions, such as pain and swelling, were also reported near the spot Beyfortus was injected. But these side effects weren’t common. They were reported in less than 1% of children receiving Beyfortus.

Both rash and injection site reactions can usually be managed at home. Ask your child’s pediatrician about what products are safe for managing these side effects.

Severe allergic reactions (such as anaphylaxis) are rare with Beyfortus, but they are possible. This can cause your child to experience hives, shortness of breath, or a blue skin color from not getting enough oxygen. Get medical help right away if your child shows symptoms of an allergic reaction after receiving Beyfortus.

Tell the healthcare professional administering Beyfortus if your child has any bleeding problems. They can make sure to use a thinner needle and prepare for more bleeding at the injection site.

Why trust our experts?

Written by:

Kristianne Hannemann, PharmD

Kristianne Hannemann, PharmD, is a licensed pharmacist in California. She has been a retail pharmacy manager and staff pharmacist for over 7 years and has contributed drug information content to different health companies.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Our editorial standards

Meet our experts