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What is RSV?

A parent’s guide to respiratory syncytial virus (RSV)

What is RSV?

What parents need to know

Respiratory Syncytial Virus (RSV) is a common and highly contagious virus that can lead to respiratory infection in babies. RSV is unpredictable, and though most of the time it will cause a mild, cold-like illness, babies can develop serious RSV lung infections. RSV spreads when droplets from a cough, sneeze, or infected surface get inside the eyes, nose, or mouth.

RSV is a leading cause of hospitalization in babies under 1.

2 out of 3 babies will get RSV by age 1.

RSV is unpredictable—it's hard to know which babies will get it or how severe it may become.

What Parents Should Know About RSV, According to Dr. Perkins

Dr. Kerry‑Anne Perkins has supported countless families as an OB‑GYN, but becoming a mom gave her a new perspective on how overwhelming RSV season can feel. She understands how unpredictable RSV can be and why parents seek trusted protection. In her story, she shares what she’s learned about RSV and how she helps parents feel confident in protecting their baby.

Watch Dr. Perkins share her medical expertise on RSV and her perspective as a mom.

“As a mom, I know how overwhelming it can be to make decisions about your baby's health, but I also know powerful it feels to have options and to feel confident in those options”

Dr. Kerry-Anne Perkins, Board Certified OB-GYN and Women’s Health Advocate

Read about Dr. Perkins’ RSV experience

DR. PERKINS: As an OB-GYN, I play a critical role in guiding expecting moms through some of the most important decisions they'll make, from preparing for birth to understanding how to protect their newborns in those early, vulnerable months.

I've had countless conversations with parents who just want to do what's best for their baby, especially when it comes to preventing illnesses like serious RSV lung infection, that's why I want to take a moment to talk about something that's giving many families peace of mind – Beyfortus.

What is Beyfortus?

It's an FDA approved preventive antibody that helps protect babies from serious lung infections caused by RSV. It was made for babies under the age of one born during or entering their first RSV season, as well as some high risk babies up to 24 months of age.

Now I want to mention that Beyfortus isn't a vaccine, it's a shot that gives your baby preventive antibodies to help guard against serious RSV lung infections.

But what's the difference between vaccines and preventive antibodies?

Vaccines are like self defense instructors. They teach the body to make its own antibodies, which means vaccines build protection over time. Beyfortus works differently. It's a preventive antibody which acts like a bodyguard. Our bodies naturally make antibodies that help us fight infections, but a baby's immune system hasn't developed enough to make the antibodies they need for protection. Beyfortus gives them these antibodies, which arms your baby with an extra layer of protection that they need while their immune system is still developing.

These antibodies are designed to stick to the RSV virus and block it from infecting your baby's lungs. That means your baby doesn't have to wait for their immune system to catch up. They're protected within days of the antibody entering their system.

When can your baby get Beyfortus?

If your baby is born in the fall or in the winter, when RSV is most common, they should receive Beyfortus at the hospital before going home or at their first well visit. If they're born in the spring or the summer, they can get it from their pediatrician at a regular well visit just before RSV season. And for babies who are at higher risk, like those born with certain health conditions, your baby's doctor may recommend a second dose before their second RSV season.

As a mom myself, I know many parents have questions about safety. Serious allergic reactions have occurred, but are extremely rare.

The most common side effects are mild to moderate, things like swelling or redness at the injection site or rash.

Why did I choose Beyfortus for my own baby?

I chose this option for my daughter after talking with her pediatrician, because I knew the preventive antibodies in Beyfortus would help provide fast-acting protection against serious RSV lung infection. I also liked the idea that my baby would be protected for five months. It gave me peace of mind, knowing she had that extra layer of protection.

So far, over 6 million babies have already received Beyfortus. But as always, if you have concerns, talk to your child's doctor.

As a mom, I know how overwhelming it can be to make decisions about your baby's health, but I also know how powerful it feels to have options and to feel confident in those options.

Why should you feel confident choosing Beyfortus for your baby?

Beyfortus is supported by the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. If you're curious about whether Beyfortus is right for your baby, I encourage you to talk to your child's doctor, ask questions, share your concerns. You deserve answers that make you feel confident.

When we're informed, we're empowered, and that's how we protect our little ones.

IMPORTANT SAFETY INFORMATION

Your child should not take Beyfortus if your child has a history of serious allergic reactions to nirsevimab-alip or any of the ingredients in Beyfortus.

Before your child receives Beyfortus, tell your healthcare provider about all of your child's medical conditions, including if your child:

  • has ever had a reaction to Beyfortus.
  • has bleeding or bruising problems. If your child has a problem with bleeding or bruises easily, an injection could cause a problem.


Tell your healthcare provider about all the medicines your child takes, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Your infant should not receive a medicine called palivizumab if they have already received Beyfortus in the same RSV season.

Serious allergic reactions have happened with Beyfortus. Get medical help right away if your child has any of the following signs or symptoms of a serious allergic reaction:

  • swelling of the face, mouth, or tongue
  • difficulty swallowing or breathing
  • unresponsiveness
  • bluish color of skin, lips, or under fingernails
  • muscle weakness
  • severe rash, hives, or itching


The most common side effects of Beyfortus include rash and pain, swelling, or hardness at the site of your child's injection. These are not all the possible side effects of Beyfortus. Call your healthcare provider if you have questions about side effects.

INDICATION

Beyfortus is a prescription medicine used to help prevent a serious lung disease caused by Respiratory Syncytial Virus (RSV) in:

  • Newborns and babies under l year of age born during or entering their first RSV season.
  • Children up to 24 months of age who remain at risk of severe RSV disease through their second RSV season.


Please see full Prescribing Information including the Patient Information at the top of this site.

The serious side of RSV

Little lungs are still developing and can be especially vulnerable to RSV.

  • For some babies RSV can escalate quickly, moving from mild cold-like symptoms to hospitalization in under a week.
  • Once admitted, the average stay is 3 to 4 days, often involving breathing support and oxygen therapy to help them recover.


Ask your baby’s doctor about Beyfortus, which can help reduce the need for medical care if your baby gets a serious RSV infection.

Baby in hospital

Simple ways to help protect your baby this RSV season

RSV is common—and while you can’t keep every germ away, there are steps you can take to help protect your little one. Here are some ways moms often help lower the risk:

Wash your hands often, and have visitors do the same before holding your baby.

Limit close contact with sick people, even if it’s “just a cold.”

Skip crowded indoor spaces during peak RSV season, especially with newborns.

Clean and disinfect surfaces and toys your baby touches often.

Ask your pediatrician about Beyfortus. It’s a one-time dose of preventive antibodies that can help protect your baby through the RSV season, typically 5 months.


Some children may need another dose if they’re still at higher risk in their second RSV season, or if they’ve had heart surgery.

A little prevention now can go a long way. These steps can help you lower your baby’s chances of getting seriously ill from RSV.


IMPORTANT SAFETY INFORMATION
IMPORTANT SAFETY INFORMATION
INDICATION
IMPORTANT SAFETY INFORMATION

Your child should not take Beyfortus if your child has a history of serious allergic reactions to nirsevimab-alip or any of the ingredients in Beyfortus.

Before your child receives Beyfortus, tell your healthcare provider about all of your child’s medical conditions, including if your child:

  • has ever had a reaction to Beyfortus.

  • has bleeding or bruising problems. If your child has a problem with bleeding or bruises easily, an injection could cause a problem.


Tell your healthcare provider about all the medicines your child takes, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Your infant should not receive a medicine called palivizumab if they have already received Beyfortus in the same RSV season.

Serious allergic reactions have happened with Beyfortus. Get medical help right away if your child has any of the following signs or symptoms of a serious allergic reaction:

  • swelling of the face, mouth, or tongue

  • difficulty swallowing or breathing

  • unresponsiveness

  • bluish color of skin, lips, or under fingernails

  • muscle weakness

  • severe rash, hives, or itching


The most common side effects of Beyfortus include rash and pain, swelling, or hardness at the site of your child’s injection. These are not all the possible side effects of Beyfortus. Call your healthcare provider if you have questions about side effects.

Please see full Prescribing Information, including Patient Information, for more details.

Click here to learn more about Sanofi’s commitment to fighting counterfeit drugs.

INDICATION

Beyfortus is a prescription medicine used to help prevent a serious lung disease caused by Respiratory Syncytial Virus (RSV) in:

  • Newborns and babies under 1 year of age born during or entering their first RSV season.

  • Children up to 24 months of age who remain at risk of severe RSV disease through their second RSV season.
MAT-US-2309454-v3.0-03/2026