RSV Shot for Babies: Beyfortus vs Enflonsia vs the Maternal Vaccine (Abrysvo)
How the three RSV protection options work, who should get which one, when to get it, how well each one worked in studies, side effects, and the questions to ask your pediatrician or OB.
What parents should know
- RSV was the leading cause of hospitalization among U.S. infants before these products arrived, according to the CDC.
- Abrysvo is the only RSV vaccine approved for pregnancy. It is given once, at 32 0/7 to 36 6/7 weeks, and protects the baby for about the first 6 months.
- Beyfortus and Enflonsia are antibodies, not vaccines. They protect the baby right away, last at least 5 months, and are given as a single shot.
- Most babies do not need both. An antibody is recommended if the mother was not vaccinated, her status is unknown, or the baby was born within 14 days of the vaccine.
- Only Beyfortus is used for the small group of high-risk children aged 8 to 19 months entering a second RSV season. The AAP widened that high-risk list in October 2026.
- In the 2024–25 season, RSV hospitalization rates in babies 0 to 7 months were 28% to 43% lower than before these products, in two CDC surveillance networks.
Why RSV protection matters for babies
Respiratory syncytial virus (RSV) causes cold-like symptoms in most people, but in young babies it can spread to the small airways and lungs and cause bronchiolitis or pneumonia. The CDC estimates that, before today's prevention products, RSV caused roughly 58,000 to 80,000 hospitalizations and 100 to 300 deaths a year among U.S. children under 5, and a 2025 CDC report notes that before universal infant protection, RSV was the leading cause of hospitalization among infants. Babies in their first few months, those born early, and those with heart or lung conditions are at the highest risk.
If you want to know what RSV looks like and when it becomes an emergency, read our guides on RSV symptoms in babies and when to worry about RSV. This guide focuses on prevention: the vaccine given in pregnancy and the two antibody shots given to babies.
The three RSV options at a glance
All three products aim at the same goal, preventing RSV lower respiratory tract infection (the lung infections that put babies in the hospital). They work in different ways and are given to different people.
| Abrysvo (maternal vaccine) | Beyfortus (nirsevimab) | Enflonsia (clesrovimab) | |
|---|---|---|---|
| Maker | Pfizer | Sanofi and AstraZeneca | Merck |
| Who gets it | Pregnant mother | Baby | Baby |
| Type | Vaccine (mother makes antibodies that cross the placenta) | Ready-made monoclonal antibody | Ready-made monoclonal antibody |
| When | 32 0/7 to 36 6/7 weeks of pregnancy, September to January in most of the U.S. | October to March; before the season or within 1 week of birth | October to March; before the season or within 1 week of birth |
| Dose | One dose (not repeated in later pregnancies at this time) | 50 mg if under 5 kg (11 lb); 100 mg if 5 kg or more | 105 mg for all eligible infants |
| Second RSV season (high-risk 8 to 19 months) | Not applicable | Yes, 200 mg | No |
| FDA approval | Pregnancy use approved August 2023 | July 2023 | June 2025 |
Option 1: The maternal RSV vaccine (Abrysvo)
Abrysvo is given to the mother during pregnancy. Her body makes antibodies against RSV, and those antibodies cross the placenta, so the baby is born already protected. The CDC says this protection lasts about 6 months after birth. Because protection fades, the vaccine is given only in a seasonal window (September through January in most of the continental U.S.) so the baby is born shortly before or during RSV season.
The timing is specific. The CDC recommends one dose at 32 0/7 through 36 6/7 weeks of gestation. After 36 weeks 6 days, there is probably not enough time for antibodies to develop and cross the placenta, so the baby should get an antibody shot instead. Pfizer's Abrysvo is the only RSV vaccine recommended in pregnancy; GSK's Arexvy and Moderna's mResvia are not approved for pregnant women. If the mother got an RSV vaccine in a previous pregnancy, the CDC does not currently recommend another dose; the new baby should get an antibody instead.
How well it worked
In the phase 3 trial of about 7,000 pregnant participants, the FDA reported that Abrysvo reduced severe RSV lower respiratory tract disease in babies by 81.8% within 90 days of birth and by 69.4% within 180 days. The CDC summarizes the same trial as a 57% lower risk of a healthcare visit for RSV and a 68% lower risk of RSV hospitalization in the first 3 months.
Safety: the preterm birth question
The Abrysvo label includes a warning about a numerical imbalance in preterm births in the main trial: 5.7% in the vaccine group versus 4.7% with placebo. The FDA says the data are insufficient to establish or exclude a cause-and-effect link. To reduce that potential risk, the vaccine is approved only from 32 through 36 weeks rather than earlier in pregnancy. In the subgroup vaccinated at 32 to 36 weeks, preterm births were 4.3% versus 3.7%. People at higher risk of preterm birth were generally excluded from the trials, so this is a good topic to raise with your OB.
Options 2 and 3: The infant RSV antibody shot (Beyfortus or Enflonsia)
Nirsevimab (Beyfortus) and clesrovimab (Enflonsia) are long-acting monoclonal antibodies. They are often called the "RSV shot" or even the "RSV vaccine" for babies, but as the CDC points out, they are not vaccines. They do not ask the baby's immune system to do anything. The antibodies themselves block the virus, so protection starts right away and lasts at least 5 months, which covers a typical RSV season.
The CDC recommends an infant antibody for babies younger than 8 months who are born during or entering their first RSV season if the mother did not get the RSV vaccine during pregnancy, her vaccination status is unknown, or the baby was born within 14 days of her vaccination. Babies born October through March should ideally get it in the first week of life, often before leaving the birth hospital. Babies born April through September should get it shortly before RSV season starts, usually October or November, and it can be given at a regular well-baby visit alongside routine vaccines.
Beyfortus vs Enflonsia: what is different?
- Dosing: Beyfortus is dosed by weight (50 mg under 5 kg, 100 mg at 5 kg or more). Enflonsia is one 105 mg dose for every eligible infant.
- Trial results: Pooled Beyfortus trials showed 79.0% efficacy against medically attended RSV lung infection and 80.6% against RSV hospitalization through 150 days. Enflonsia's trial showed 60.4% against medically attended RSV lung infection and 90.9% against RSV hospitalization through 150 days. These were separate trials with different designs, so the numbers cannot be compared head to head.
- Real-world data: Beyfortus has been used since the 2023–24 season. The CDC says early real-world data show it was at least 70% effective at preventing RSV hospitalization.
- Second season: Only Beyfortus is approved and recommended for high-risk children 8 to 19 months entering their second RSV season.
- Preference: Neither the CDC's advisory committee nor the AAP prefers one product for first-season babies. The choice usually comes down to what your pediatrician or hospital stocks.
Vaccine in pregnancy or antibody after birth: how to choose
The CDC asks clinicians to discuss both options with families and consider their preferences. There is no single right answer, but these points usually decide it:
- Your due date. If you will be 32 to 36 weeks pregnant between September and January, the maternal vaccine is an option. If you are due in spring or summer, or you are past 36 weeks 6 days, your baby will get the antibody instead.
- Protection at birth. The maternal vaccine protects the baby from the moment of birth, as long as delivery is at least 14 days after the shot. The antibody protects from the day it is given.
- Not giving the baby a shot. Some parents prefer the maternal vaccine so the newborn does not need an extra injection. Others prefer the antibody so nothing is given during pregnancy.
- Previous RSV vaccine. If you were vaccinated in an earlier pregnancy, the CDC currently recommends the antibody for this baby rather than a second vaccine dose.
- Health conditions. Babies whose mothers may not respond well to vaccination (for example, immune problems or HIV) or babies with serious heart disease may be considered for an antibody even after maternal vaccination.
Which children need RSV protection in a second season?
Most children do not need RSV immunization after 8 months of age, and the CDC says children 8 months and older who are not at increased risk should not receive it. A small group of children aged 8 through 19 months who are entering their second RSV season are recommended to get Beyfortus (200 mg, given as two 100 mg injections), regardless of what they or their mother received before.
In its policy statement published October 26, 2026, the AAP expanded its high-risk list for the 2026–27 season. Along with the groups the CDC already lists (chronic lung disease of prematurity that needed medical support in the past 6 months, severe immunocompromise, cystic fibrosis with severe lung disease or low weight-for-length, and American Indian and Alaska Native children), the AAP now also includes:
- Children born before 32 weeks of gestation, regardless of whether they needed medicines or oxygen
- Children with hemodynamically significant congenital heart disease
- Children with anatomic lung abnormalities or neuromuscular disorders that raise RSV risk
- Children with Down syndrome or other chromosomal differences that raise RSV risk
Side effects and safety
For the infant antibodies, the CDC says side effects are usually mild, such as pain, redness or swelling where the shot was given, and go away quickly. Allergic reactions are uncommon but have been reported with similar antibody products. Both antibodies should not be given to a child who has had a severe allergic reaction (such as anaphylaxis) to any ingredient. They can be given at the same visit as routine childhood vaccines, and no spacing is needed before live vaccines such as MMR or chickenpox.
For the maternal vaccine, the most common side effects in pregnant participants were pain at the injection site, headache, muscle pain and nausea, according to the FDA label. It can be given at the same visit as Tdap, flu or COVID-19 vaccines. See our overview of common vaccine side effects in babies for general tips on comforting your baby after any shot.
Is the RSV antibody still recommended in 2026?
Yes. The CDC's RSV clinical guidance and the AAP both recommend an infant RSV antibody for babies under 8 months whose mothers were not vaccinated (or whose status is unknown, or who were born within 14 days of vaccination). In January 2026, HHS reorganized the CDC childhood schedule into three groups and placed RSV monoclonal antibodies under immunizations for "high-risk groups." In practice, the target group is still the same: babies who are not already protected through maternal vaccination. The AAP publishes its own schedule and continues to recommend RSV immunization for all infants under 8 months without documented maternal protection.
Is it working? A CDC analysis of the 2024–25 season, the first with wide availability of both the maternal vaccine and nirsevimab, found RSV hospitalization rates among babies 0 to 7 months were 43% lower (RSV-NET) and 28% lower (NVSN) than in the 2018–2020 seasons, with the biggest drop, about half, in babies 0 to 2 months. That kind of before-and-after comparison cannot prove cause and effect for any single baby, but it matches what the trials showed.
Even with protection, when should you call the doctor?
No product prevents every RSV infection. Protected babies can still catch RSV, though they are much less likely to get severely ill. Keep the usual habits that lower risk during the season: wash hands, keep sick visitors away from newborns, avoid smoke exposure, and keep up with routine vaccines (see our baby vaccine schedule guide).
Call your pediatrician right away, or seek emergency care, if your baby is breathing fast, the skin pulls in between or under the ribs with each breath, they grunt or flare their nostrils, the lips or face look bluish or gray, they pause in breathing, they are not feeding or have far fewer wet diapers, or a baby under 3 months has a fever of 100.4°F (38°C) or higher. Our bronchiolitis guide explains home care for milder cases.
Frequently asked questions
Does my baby need the RSV shot if I got the RSV vaccine while pregnant?
Usually not. If you received Abrysvo during this pregnancy and your baby was born at least 14 days later, most babies do not need Beyfortus or Enflonsia. Your pediatrician may still recommend it in rare cases, such as serious heart disease or certain maternal immune conditions.
Is Beyfortus or Enflonsia better?
Neither the CDC's advisory committee nor the AAP prefers one. Both are single shots that protect for at least 5 months. Enflonsia is one fixed dose; Beyfortus is dosed by weight and is the only one used for high-risk children in a second RSV season.
When should my baby get the RSV antibody?
Babies born October through March should get it within the first week of life, ideally before leaving the hospital. Babies born April through September should get it shortly before RSV season, usually in October or November.
Is the RSV antibody a vaccine?
No. Nirsevimab and clesrovimab are ready-made monoclonal antibodies. They protect the baby directly instead of training the immune system, which is why protection starts right away and fades after the season.
When can I get the RSV vaccine during pregnancy?
The CDC recommends one dose of Pfizer's Abrysvo at 32 0/7 through 36 6/7 weeks of pregnancy, given September through January in most of the continental U.S. Other RSV vaccines are not approved for pregnancy.
What are the side effects of the RSV shot for babies?
The CDC says side effects are usually mild, such as pain, redness or swelling at the injection site, and resolve quickly. Allergic reactions are uncommon. Do not give it to a child who has had a severe allergic reaction to its ingredients.
Can my baby still get RSV after the shot?
Yes, but severe illness is much less likely. In trials, the antibodies reduced RSV hospitalization by roughly 81% to 91% over about five months. Watch for breathing trouble, poor feeding and fever in young babies, and call your pediatrician if you see them.
Keep reading
Sources
This guide was checked against the current guidance below. Medical and safety recommendations can change; use the linked source and your child's clinician for decisions specific to your family.
- CDC: RSV in infants and young children
- CDC: RSV immunization guidance for infants and young children
- CDC: RSV vaccine guidance for pregnant women
- CDC: Immunizations to protect infants from RSV
- MMWR (2025): Use of clesrovimab for prevention of severe RSV in infants, ACIP recommendations
- MMWR (2025): RSV hospitalization rates among infants after introduction of RSV prevention products, 2024-25
- AAP (October 2026): Recommendations for the prevention of RSV disease in infants and children, policy statement
- FDA: FDA approves first vaccine for pregnant individuals to prevent RSV in infants
- FDA: Abrysvo prescribing information
- HHS (January 2026): Decision memo adopting the revised childhood and adolescent immunization schedule
- CDC: ACIP vaccine recommendations (June 2025 RSV vote)