RSV in Babies: 2026-27 Guide (Beyfortus, Symptoms, When to Worry)

Your baby's cold is on day 3, and something about the cough sounds different. RSV (respiratory syncytial virus) is the leading cause of hospitalization in U.S. infants, and in babies under 6 months, a virus that looks like a bad cold can quickly turn into hard breathing. For the 2026-27 season, families also have real news to work with: two long-acting antibody shots for babies (Beyfortus and the new Enflonsia) and a maternal RSV vaccine (Abrysvo) during pregnancy.

What is RSV?

RSV is a common respiratory virus that infects the nose, throat, airways, and lungs. In babies, it is the leading cause of both hospitalization and bronchiolitis (inflammation of the small airways). Almost every child in the U.S. has been infected with RSV at least once by age 2, according to the American Academy of Pediatrics. Most kids only get a cold-like illness. The risk of severe disease is highest in babies under 6 months, in preemies, and in babies with heart or lung conditions or a weakened immune system.

How RSV differs from a common cold

In the first day or two, RSV, a cold, the flu, and COVID can look alike. What sets RSV apart in babies is its higher tendency to move into the lower airways and cause wheezing, fast breathing, and trouble feeding. If your baby's cough sounds wet or rattly, or you can see the chest working hard with each breath, have a pediatrician take a look.

RSV Symptoms in Babies and Toddlers

Typical RSV symptoms include a runny nose, coughing, sneezing, low appetite, and sometimes a mild fever. Wheezing (a high-pitched whistle when your baby breathes out) can appear as the illness moves lower. Symptoms usually show up 4 to 6 days after exposure and peak on days 3 through 5.

One note from the CDC: in very young infants, the only signs of RSV may be irritability, low activity, and breathing difficulty. Classic cold symptoms can be missing. A baby who is fussier than usual and feeding poorly deserves a call, even without a cough.

Symptoms by age (under 6 months, 6 to 24 months, 2 years and older)

• Under 6 months: poor feeding, sleepiness, irritability, and hard or fast breathing may be the only clues. Highest risk of hospitalization.
• 6 to 24 months: more classic cold symptoms plus cough and possible wheezing. Watch for chest working hard, refusal to feed, or fewer wet diapers.
• 2 years and older: usually looks like a cold. Serious illness is much less common at this age.

When RSV Season Peaks in 2026-27

Based on CDC surveillance, RSV season in the U.S. runs from fall through spring, with a historical peak window of November through February. Southern states like Florida often see an earlier start. Northern states typically peak in January or February.

The CDC has not yet published a formal outlook for 2026-27. The 2025-26 season started earlier than usual, so it is worth being ready by October. For live regional activity, see the CDC RSV surveillance page at cdc.gov/rsv/php/surveillance. A simple parent timeline:

• September to October: ask your pediatrician about Beyfortus or Enflonsia for the baby, or Abrysvo if you are still pregnant. Start winter handwashing habits.
• November to February: peak vigilance. This is when most RSV hospitalizations happen. Watch for the warning signs below.
• March to April: the season is winding down, but RSV can still circulate.

How RSV Spreads

RSV spreads through coughs, sneezes, and close contact like kissing a baby's face. It also spreads on hands and surfaces. The virus can live for several hours on hard surfaces like doorknobs, cribs, and toys, which is why handwashing is one of the strongest prevention tools during RSV season.

People are usually contagious for 3 to 8 days, sometimes starting a day or two before symptoms appear. Very young infants and people with weak immune systems can shed the virus for as long as 4 weeks. Fever going away does not mean the baby has stopped shedding.

How RSV Is Diagnosed

Most RSV cases are diagnosed at the doctor's office based on a physical exam and your baby's symptoms. A pediatrician listens to the chest, watches how hard the baby is working to breathe, and checks feeding and diaper counts. Nasal swab tests (antigen or PCR) can confirm RSV but are usually done in the hospital, not for a typical mild case. On a Blueberry video visit, we can watch your baby breathe and help you decide whether the next step is home care, a same-day in-person visit, or the ER.

How RSV Is Treated at Home

Most healthy babies recover from RSV at home in 1 to 2 weeks with supportive care. There is no antibiotic for RSV (antibiotics do not work on viruses), and there is no specific antiviral drug for RSV in babies. Home care is about keeping the airways clear, the feeds going in, and the baby comfortable.

Home care that helps:

• Saline drops and gentle suction. A few drops of saline in the nose, then a bulb syringe or a Nose Frida, can help before feeds and sleep.
• Small, frequent feeds. Offer breast milk or formula more often than usual - that stays the main source of both calories and fluids. For babies over 6 months, small sips of water are fine in addition.
• A cool-mist humidifier in the room your baby sleeps in.
• Fever control if needed. Follow the label for infant acetaminophen. Ibuprofen is for babies 6 months and older. Never use aspirin in a child.
• Upright holding. Babies breathe more easily when held upright.

What does not help: over-the-counter cough and cold medicines in young children (the FDA and AAP both advise against them), and antibiotics.

Warning Signs, When to Call Your Pediatrician

Call your pediatrician the same day (do not wait) if you see any of the following. These are the "call today" signs the CDC and the AAP flag for RSV.

• Working harder to breathe. Faster breathing than usual, or you can see the chest and belly working hard.
• Poor feeding. Taking much less than usual for more than a day, or refusing feeds.
• Fewer wet diapers. Fewer than one wet diaper every 8 hours is the AAP's early dehydration threshold.
• Fever of 100.4°F or higher in a baby under 3 months. Always an urgent call, RSV or not.
• A fever over 104°F, or a fever that keeps getting worse at any age.
• A cough that sounds wet or rattly, or a new wheeze (a high-pitched whistle on exhale).
• Not improving after about a week, or clearly worsening after day 3 to 5.
• Much less active or alert than usual.

On a Blueberry video visit, we can watch your baby's chest and belly move together and usually tell you within a few minutes whether it is a home-care situation or a same-day visit.

When to Go to the ER

Some signs need emergency care right away. Call 911 for the top two red flags below. Go to the ER for the rest. Do not wait to see if it improves on its own.

• Bluish, gray, or pale skin, lips, or nail beds (a sign of low oxygen). Call 911.
• Pauses in breathing (apnea), especially in a baby under 3 months. Call 911.
• Severe retractions. The skin visibly caves in between the ribs, below the ribcage, or above the collarbone with each breath.
• Nasal flaring with every breath, or grunting on exhale.
• Extreme sleepiness or floppiness. Baby is limp, hard to wake, or not making eye contact.
• Severe dehydration. No wet diaper for 8 hours or longer together with no tears when crying or a sunken soft spot on the head.
• Oxygen reading below about 90 percent on a home pulse oximeter, especially if the baby also looks in distress.

If your baby is under 3 months old and having any breathing trouble at all, go to the ER. A telehealth visit is not the right tool for that.

The quick side-by-side:

How to Prevent RSV in Your Baby

Prevention this season combines immunization (covered below) with everyday habits that lower spread:

• Handwashing before touching the baby, and asking visitors to do the same.
• Keeping sick contacts (including older siblings with a cold) away from the baby when possible.
• Avoiding tobacco smoke and vape exposure. Both raise the risk of severe RSV.
• Breastfeeding if you can. Breast milk passes on some protective antibodies.
• Cleaning shared surfaces (crib rails, toys, doorknobs) during peak season.

For more on winter respiratory illnesses beyond RSV, see our companion piece on how to keep babies and toddlers safe from RSV, flu, and winter germs.

Beyfortus (Nirsevimab) and Enflonsia, 2026-27 Guidance

For the 2026-27 season, the CDC recommends one of two paths to protect a baby's first RSV season: the maternal RSV vaccine (Abrysvo) during pregnancy, or one dose of a long-acting monoclonal antibody for the baby after birth. Most babies need one path, not both.

The two baby options are Beyfortus (nirsevimab) and Enflonsia (clesrovimab). Neither one is a vaccine. A vaccine trains the immune system to make its own antibodies; these shots deliver ready-made antibodies directly, and one dose protects for a full RSV season.

What are Beyfortus and Enflonsia, and how do they work?

Beyfortus (nirsevimab, made by Sanofi and AstraZeneca) has been FDA-approved and CDC-recommended since 2023. One shot gives a baby ready-made RSV antibodies that protect through the whole season (about 5 months).

Enflonsia (clesrovimab, made by Merck) is the other option, added to the CDC's recommendation in June 2025. It works the same way and covers the same first-season window. The CDC does not prefer one over the other. Your pediatrician will use whichever is available in your area.

Which infants are eligible for the 2026-27 season?

Both Beyfortus and Enflonsia are recommended for infants younger than 8 months entering their first RSV season, if their mother did not get the Abrysvo vaccine during pregnancy at least 14 days before delivery, or if her vaccination status is not known.

A smaller group of children ages 8 to 19 months at increased risk of severe RSV may also get a second-season dose of Beyfortus. (Enflonsia is first-season only.) Increased-risk groups include children with chronic lung disease of prematurity who needed ongoing medical support, severe immunocompromise, cystic fibrosis with severe lung disease or poor growth, and American Indian or Alaska Native children.

Beyfortus vs. the maternal RSV vaccine (Abrysvo)

Abrysvo is a vaccine given to the pregnant person between 32 weeks and the end of 36 weeks of pregnancy (through 36 weeks and 6 days), from September through January. The mother's antibodies cross the placenta and protect the newborn for the first few months. The two paths lead to the same goal (a protected first season):

• Path A, before birth: the pregnant person gets Abrysvo. If the shot is given at least 14 days before delivery, the baby usually does not need an antibody shot.
• Path B, after birth: the baby gets one dose of Beyfortus or Enflonsia.

Ask your pediatrician which path fits your family. If your baby was born within 14 days of the mother's Abrysvo dose, or you were unable to get the vaccine, the baby is still eligible for the antibody shot.

Beyfortus vs. Synagis (palivizumab), a historical note

Synagis (palivizumab) was the older RSV monoclonal antibody. It required a shot every month during RSV season and was only used for very-high-risk infants. According to the CDC, Synagis was discontinued at the end of December 2025. For the 2026-27 season, Beyfortus and Enflonsia have replaced it. Both are single-dose shots that cover the whole season, and both are recommended for a much broader group of infants, not just the highest-risk babies.

Timing, safety, and side effects

Beyfortus and Enflonsia are given from October through the end of March in most of the continental U.S. Babies born during the season should ideally get the shot within a week of birth, often during the hospital stay. Babies born in spring or summer get the shot in the fall, just before the season starts.

The most common side effects are mild: pain, redness, or swelling where the shot was given, and sometimes a rash. Serious allergic reactions are uncommon but have been reported with antibody shots like these. No new safety concerns have come out of post-marketing surveillance to date. Both shots can be given at the same visit as routine baby vaccines. In studies, both Beyfortus and Enflonsia lowered the chance of a baby being hospitalized with RSV by roughly 80 percent or more. The two shots were not tested against each other, and the CDC does not recommend one over the other.

Source: CDC RSV Immunizations for Infants and Young Children (HCP guidance); ACIP MMWR 2023 (nirsevimab) and 2025 (clesrovimab).

Frequently Asked Questions About RSV in Babies

Does RSV resolve on its own?

For most healthy babies, yes. Most infants recover at home in 1 to 2 weeks with supportive care. But this is not a blanket "let it run its course" answer. Infants under 6 months, preemies, and babies with heart or lung conditions are at real risk of severe disease and hospitalization, so watch closely for the warning signs above and call your pediatrician if any of them appear.

What is a normal oxygen level for a baby?

For a healthy baby awake or asleep, oxygen saturation is generally in the mid to high 90s. A reading below about 90 percent is a concerning sign, but home infant pulse oximeters are often inaccurate on wiggly babies, and readings can dip briefly during sleep and return to normal. Use the clinical picture more than any single number, and never let a normal number reassure you if the baby looks unwell.

How long is RSV contagious?

People with RSV are usually contagious for 3 to 8 days, sometimes starting a day or two before symptoms appear. Very young infants and immunocompromised people can shed the virus for up to 4 weeks. Fever going away does not mean the baby has stopped shedding.

Can adults catch RSV from babies?

Yes. RSV circulates in all ages. Healthy adults usually get a cold-like illness. RSV can be more serious in older adults and adults with chronic heart or lung conditions.

What is the difference between Beyfortus and Synagis?

The long-acting antibodies (Beyfortus and Enflonsia) are single-dose, season-long RSV shots recommended broadly for infants under 8 months. Synagis (palivizumab) was the older monthly RSV shot for very-high-risk infants only, and was discontinued at the end of December 2025. For the 2026-27 season, these long-acting antibodies have replaced it.

When does RSV season peak in 2026-27?

Historically the U.S. RSV peak is November through February. The CDC has not yet published a formal outlook for the 2026-27 season, and recent seasons have started earlier than usual, so it is worth being ready by October. Check cdc.gov/rsv/php/surveillance for live regional activity during the season.

When to Talk to a Blueberry Pediatrician

Most of the RSV-season calls we take at Blueberry sound the same: it is late, the baby has a wet-sounding cough, and the parent is trying to decide between "let's see how the night goes" and "we should go in." A short video visit is usually enough: a pediatrician can watch how your baby is breathing, listen through the app, and give you a plan for the next few hours.

For anything on the ER red-flag list above, go straight to the ER or call 911. For everything in between, we can help you decide the next step in a few minutes.

Sources: CDC RSV clinical guidance (nirsevimab, clesrovimab, palivizumab discontinuation), CDC RSV surveillance and About RSV, ACIP MMWR 2023 (nirsevimab), ACIP MMWR 2025 (clesrovimab), ACIP MMWR 2023 (Abrysvo maternal vaccine), AAP Recommended Immunization Schedule 2026, AAP HealthyChildren.org RSV guidance, ACOG maternal RSV vaccination practice advisory, and Payne AB, et al., “Effectiveness of nirsevimab among infants in their first RSV season in the United States, October 2023–March 2024: a test-negative design analysis,” Lancet Regional Health – Americas, 2025.