Respiratory syncytial virus (RSV) infection is nearly universal in early childhood. Before the newest prevention options became available, an estimated 2%–3% of infants younger than 3 months of age — most otherwise healthy — were hospitalized with RSV each year. That began to change in 2023 with the introduction of maternal vaccination and long-acting antibodies for infants.
For the 2026–2027 RSV season, clinicians and families have three options for protecting infants during their first RSV season:
- Maternal RSV vaccine (Abrysvo) — Maternal vaccination was first recommended in the United States in 2023. It can be administered between 32 weeks and 36 weeks of pregnancy when babies will be born during RSV season. Generally, vaccinations are recommended between September and January. Antibodies produced by the mother cross the placenta to protect the baby immediately after birth. This approach is currently only recommended as a one-time option, so babies born during subsequent pregnancies would be eligible for protection using the tools described below.
- Nirsevimab (Beyfortus) — Widespread use of passive immunization of babies became a more feasible option when Beyfortus became available in 2023. This long-acting antibody is administered to eligible infants younger than 8 months of age born during or entering their first RSV season. Passive immunization is not needed for most babies if their mothers were vaccinated at least two weeks prior to delivery. This tool is also recommended for certain high-risk children entering their second RSV season.
- Clesrovimab (Enflonsia) was FDA-approved and recommended in 2025. It is another long-acting antibody, providing a second option for administration to eligible infants during their first RSV season. It is not currently approved or recommended for high-risk children entering their second RSV season.
As experience with these products accumulates, ongoing studies are informing what we know, making it easier for providers to answer questions from patients and families. This month, we wanted to provide the latest information in the form of common questions we are hearing from families.
Nirsevimab wasn’t available for my first child in 2022, but I’m due with another baby this fall. How well is it working?
Responding to families
Nirsevimab has been used for three seasons now, and our experience has been highly reassuring. Infants who received nirsevimab have had fewer RSV-related emergency department visits, hospitalizations, and admissions to intensive care units. It’s important to be aware that the goal of these antibody products is not to eliminate RSV, but rather, to prevent more serious illness so that babies don’t end up in the emergency room or hospital.
Check out the data
- A multistate study published in MMWR included 759 infants admitted to 27 intensive care units. Nirsevimab was about 80% effective against RSV-associated intensive care admission and 83% effective against respiratory failure, which was defined as illness requiring support in the form of positive airway pressure or invasive ventilation.
- A study in published in The Lancet Regional Health – Americas, used data from six health systems, to estimate that receipt of the antibody product decreased RSV-associated emergency department visits by about 77%.
- A systematic review published in The Lancet Child & Adolescent Health found estimated effectiveness against hospitalization to be between 74% and 85%. Although the studies differed in designs, populations and settings, they consistently found that nirsevimab substantially reduced hospitalization and critical illness.
What about the maternal RSV vaccine? Is it helping infants as much as the trials predicted?
Responding to families
Maternal RSV vaccination is working well in routine practice. It is reducing hospitalizations in babies. For those who still get infected, their illness is milder, and if hospitalized, they have shorter stays. Knowing that it is very challenging to develop vaccines that can prevent infections like RSV, it is reassuring to see this vaccine working to protect babies when received by their mothers during pregnancy.
Check out the data
- A national Scottish study, published in Lancet Infectious Disease, included about 27,000 infants. Vaccination of mothers during pregnancy was estimated to be about 82.2% effective against RSV hospitalization of infants during the first 90 days of life.
- A multicenter US study in JAMA Pediatrics was designed to study the population-based impact of RSV prevention strategies by better understanding the characteristics of almost 5,000 infants hospitalized with respiratory infections. Infants born to vaccinated mothers (n=133) were compared to infants born to unvaccinated mothers (n=313), and vaccine effectiveness was estimated to be about 70% against RSV hospitalization among infants younger than 6 months of age.
- An Argentinian study published in Pediatric Infectious Diseases Journal reached a similar conclusion. It estimated that maternal vaccination was 78.7% effective against RSV hospitalization of the infant after adjusting for infant age, prematurity, and chronic respiratory disease. Infants who developed RSV despite maternal vaccination required fewer days of oxygen and had shorter hospital stays.
I’m pregnant with my first child. A friend told me the maternal RSV vaccine causes preterm birth. Is that true?
Responding to families
This is a common question that is based in our experience during clinical trials. The original clinical trials had more preterm births among women in the vaccinated group compared with the control group, although the numbers were not statistically significant. Two things are important to know about this:
- Because of the possibility of a causal association, the FDA limited vaccination to 32 through 36 weeks of pregnancy to reduce the chance for premature births.
- Safety monitoring studies performed after authorization have not found an association.
Check out the data
- A French national study in Obstetrics & Gynecology matched nearly 25,000 women vaccinated during pregnancy with 25,000 women who were not vaccinated. They found no increase in preterm births, stillbirths, impaired fetal growth, preeclampsia, hemorrhage, or major maternal cardiovascular problems after vaccination compared with no vaccination.
- A US analysis published in JAMA matched 6,857 vaccinated to 6,857 unvaccinated women. No increased risk of preterm birth, early rupture of membranes, or pregnancy-related high blood pressure was found among those who were vaccinated compared with those who were not.
My delivery hospital immunizes infants with clesrovimab, but my pediatrician uses nirsevimab. How are they different, and should I ask for one over the other?
Responding to families
For an eligible infant in the first RSV season, either product is a good option. Clesrovimab and nirsevimab work in similar ways. Both provide infants with antibodies that offer immediate protection against RSV. The antibodies in the two products attach to different parts of the RSV protein important for infection (fusion protein), but that difference has not been demonstrated to cause a difference in how well each product works. For this reason, either is recommended for use without preference for one over the other. Notably, clinical trials cannot typically be compared because studies are designed differently, done at different times, and may measure outcomes differently. While real-world effectiveness data are already available for nirsevimab, comparable data for the newer clesrovimab are still emerging.
Check out the data
The practical differences are largely about dosing and logistics, detailed in the American Academy of Pediatrics policy statement on recommendations for prevention of RSV disease:
- Clesrovimab uses the same dose for all eligible first-season infants, regardless of weight, whereas nirsevimab dosing during the first season depends on the infant’s weight.
- Only nirsevimab is currently recommended for certain high-risk children entering a second RSV season. Clesrovimab remains under review for this application as of August 19, 2026.
Updated 2026 guidance is anticipated to be published by AAP at the start of RSV season.
How should I choose between maternal vaccination and an infant antibody? Is one better?
Responding to families
Both approaches substantially reduce the chance that your baby will experience severe RSV disease. The choice usually depends on timing, availability, medical circumstances and personal preference.
Maternal vaccination may be preferred when a family is interested in protecting the baby from birth without requiring an infant injection. It can usually be given during a prenatal visit or at a pharmacy. Some families value knowing that their baby will arrive with protection already in place.
An infant antibody is best for families who prefer direct administration of antibodies at levels known to be protective. There are also scenarios in which these products become the only option available, including when:
- Fewer than 14 days remain between maternal vaccination and delivery.
- Maternal vaccination cannot be given due to a medical contraindication, including administration during a prior pregnancy.
- The baby has already been born without protection from maternal vaccination, including those born outside of RSV season when maternal vaccine was not option.
Check out the data
Data to support preference for one strategy over another based on infant outcomes alone are limited. For this reason, current U.S. guidance does not favor one over the other.
- A French study compared the strategies directly. In one study of 42,560 infants, nirsevimab was associated with a 26% lower relative risk of RSV hospitalization compared with maternal vaccination. It’s important to note that this study was observational rather than randomized, so families chose their RSV prevention strategy. Differences between the families who selected each strategy may have affected the results.
Wrap-up
A clinician’s recommendation remains one of the strongest influences on acceptance. Families benefit from a clear explanation of RSV severity, safety, expected duration of protection, timing, and local product availability.
Maternal vaccination, nirsevimab, and clesrovimab all substantially reduce severe RSV disease. For most families, the best strategy is the one for which the infant is eligible, can be provided at the right time, and fits the family’s preferences and circumstances.
Resources
- Protecting Babies from RSV: What You Should Know
- Respiratory Syncytial Virus (RSV): The Disease, Vaccines & Monoclonal Antibody: webpage | video | podcast
- RSV: On the Go
Contributed by: Lori Handy, MD, MSCE , Charlotte A. Moser, MS, Paul A. Offit, MD
Respiratory syncytial virus (RSV) infection is nearly universal in early childhood. Before the newest prevention options became available, an estimated 2%–3% of infants younger than 3 months of age — most otherwise healthy — were hospitalized with RSV each year. That began to change in 2023 with the introduction of maternal vaccination and long-acting antibodies for infants.
For the 2026–2027 RSV season, clinicians and families have three options for protecting infants during their first RSV season:
- Maternal RSV vaccine (Abrysvo) — Maternal vaccination was first recommended in the United States in 2023. It can be administered between 32 weeks and 36 weeks of pregnancy when babies will be born during RSV season. Generally, vaccinations are recommended between September and January. Antibodies produced by the mother cross the placenta to protect the baby immediately after birth. This approach is currently only recommended as a one-time option, so babies born during subsequent pregnancies would be eligible for protection using the tools described below.
- Nirsevimab (Beyfortus) — Widespread use of passive immunization of babies became a more feasible option when Beyfortus became available in 2023. This long-acting antibody is administered to eligible infants younger than 8 months of age born during or entering their first RSV season. Passive immunization is not needed for most babies if their mothers were vaccinated at least two weeks prior to delivery. This tool is also recommended for certain high-risk children entering their second RSV season.
- Clesrovimab (Enflonsia) was FDA-approved and recommended in 2025. It is another long-acting antibody, providing a second option for administration to eligible infants during their first RSV season. It is not currently approved or recommended for high-risk children entering their second RSV season.
As experience with these products accumulates, ongoing studies are informing what we know, making it easier for providers to answer questions from patients and families. This month, we wanted to provide the latest information in the form of common questions we are hearing from families.
Nirsevimab wasn’t available for my first child in 2022, but I’m due with another baby this fall. How well is it working?
Responding to families
Nirsevimab has been used for three seasons now, and our experience has been highly reassuring. Infants who received nirsevimab have had fewer RSV-related emergency department visits, hospitalizations, and admissions to intensive care units. It’s important to be aware that the goal of these antibody products is not to eliminate RSV, but rather, to prevent more serious illness so that babies don’t end up in the emergency room or hospital.
Check out the data
- A multistate study published in MMWR included 759 infants admitted to 27 intensive care units. Nirsevimab was about 80% effective against RSV-associated intensive care admission and 83% effective against respiratory failure, which was defined as illness requiring support in the form of positive airway pressure or invasive ventilation.
- A study in published in The Lancet Regional Health – Americas, used data from six health systems, to estimate that receipt of the antibody product decreased RSV-associated emergency department visits by about 77%.
- A systematic review published in The Lancet Child & Adolescent Health found estimated effectiveness against hospitalization to be between 74% and 85%. Although the studies differed in designs, populations and settings, they consistently found that nirsevimab substantially reduced hospitalization and critical illness.
What about the maternal RSV vaccine? Is it helping infants as much as the trials predicted?
Responding to families
Maternal RSV vaccination is working well in routine practice. It is reducing hospitalizations in babies. For those who still get infected, their illness is milder, and if hospitalized, they have shorter stays. Knowing that it is very challenging to develop vaccines that can prevent infections like RSV, it is reassuring to see this vaccine working to protect babies when received by their mothers during pregnancy.
Check out the data
- A national Scottish study, published in Lancet Infectious Disease, included about 27,000 infants. Vaccination of mothers during pregnancy was estimated to be about 82.2% effective against RSV hospitalization of infants during the first 90 days of life.
- A multicenter US study in JAMA Pediatrics was designed to study the population-based impact of RSV prevention strategies by better understanding the characteristics of almost 5,000 infants hospitalized with respiratory infections. Infants born to vaccinated mothers (n=133) were compared to infants born to unvaccinated mothers (n=313), and vaccine effectiveness was estimated to be about 70% against RSV hospitalization among infants younger than 6 months of age.
- An Argentinian study published in Pediatric Infectious Diseases Journal reached a similar conclusion. It estimated that maternal vaccination was 78.7% effective against RSV hospitalization of the infant after adjusting for infant age, prematurity, and chronic respiratory disease. Infants who developed RSV despite maternal vaccination required fewer days of oxygen and had shorter hospital stays.
I’m pregnant with my first child. A friend told me the maternal RSV vaccine causes preterm birth. Is that true?
Responding to families
This is a common question that is based in our experience during clinical trials. The original clinical trials had more preterm births among women in the vaccinated group compared with the control group, although the numbers were not statistically significant. Two things are important to know about this:
- Because of the possibility of a causal association, the FDA limited vaccination to 32 through 36 weeks of pregnancy to reduce the chance for premature births.
- Safety monitoring studies performed after authorization have not found an association.
Check out the data
- A French national study in Obstetrics & Gynecology matched nearly 25,000 women vaccinated during pregnancy with 25,000 women who were not vaccinated. They found no increase in preterm births, stillbirths, impaired fetal growth, preeclampsia, hemorrhage, or major maternal cardiovascular problems after vaccination compared with no vaccination.
- A US analysis published in JAMA matched 6,857 vaccinated to 6,857 unvaccinated women. No increased risk of preterm birth, early rupture of membranes, or pregnancy-related high blood pressure was found among those who were vaccinated compared with those who were not.
My delivery hospital immunizes infants with clesrovimab, but my pediatrician uses nirsevimab. How are they different, and should I ask for one over the other?
Responding to families
For an eligible infant in the first RSV season, either product is a good option. Clesrovimab and nirsevimab work in similar ways. Both provide infants with antibodies that offer immediate protection against RSV. The antibodies in the two products attach to different parts of the RSV protein important for infection (fusion protein), but that difference has not been demonstrated to cause a difference in how well each product works. For this reason, either is recommended for use without preference for one over the other. Notably, clinical trials cannot typically be compared because studies are designed differently, done at different times, and may measure outcomes differently. While real-world effectiveness data are already available for nirsevimab, comparable data for the newer clesrovimab are still emerging.
Check out the data
The practical differences are largely about dosing and logistics, detailed in the American Academy of Pediatrics policy statement on recommendations for prevention of RSV disease:
- Clesrovimab uses the same dose for all eligible first-season infants, regardless of weight, whereas nirsevimab dosing during the first season depends on the infant’s weight.
- Only nirsevimab is currently recommended for certain high-risk children entering a second RSV season. Clesrovimab remains under review for this application as of August 19, 2026.
Updated 2026 guidance is anticipated to be published by AAP at the start of RSV season.
How should I choose between maternal vaccination and an infant antibody? Is one better?
Responding to families
Both approaches substantially reduce the chance that your baby will experience severe RSV disease. The choice usually depends on timing, availability, medical circumstances and personal preference.
Maternal vaccination may be preferred when a family is interested in protecting the baby from birth without requiring an infant injection. It can usually be given during a prenatal visit or at a pharmacy. Some families value knowing that their baby will arrive with protection already in place.
An infant antibody is best for families who prefer direct administration of antibodies at levels known to be protective. There are also scenarios in which these products become the only option available, including when:
- Fewer than 14 days remain between maternal vaccination and delivery.
- Maternal vaccination cannot be given due to a medical contraindication, including administration during a prior pregnancy.
- The baby has already been born without protection from maternal vaccination, including those born outside of RSV season when maternal vaccine was not option.
Check out the data
Data to support preference for one strategy over another based on infant outcomes alone are limited. For this reason, current U.S. guidance does not favor one over the other.
- A French study compared the strategies directly. In one study of 42,560 infants, nirsevimab was associated with a 26% lower relative risk of RSV hospitalization compared with maternal vaccination. It’s important to note that this study was observational rather than randomized, so families chose their RSV prevention strategy. Differences between the families who selected each strategy may have affected the results.
Wrap-up
A clinician’s recommendation remains one of the strongest influences on acceptance. Families benefit from a clear explanation of RSV severity, safety, expected duration of protection, timing, and local product availability.
Maternal vaccination, nirsevimab, and clesrovimab all substantially reduce severe RSV disease. For most families, the best strategy is the one for which the infant is eligible, can be provided at the right time, and fits the family’s preferences and circumstances.
Resources
- Protecting Babies from RSV: What You Should Know
- Respiratory Syncytial Virus (RSV): The Disease, Vaccines & Monoclonal Antibody: webpage | video | podcast
- RSV: On the Go
Contributed by: Lori Handy, MD, MSCE , Charlotte A. Moser, MS, Paul A. Offit, MD