Syncytial Virus In Infants Research Articles

Provider Guidance for the Prevention of Respiratory Syncytial Virus in Infants: Maternal Vaccination Versus Infant Monoclonal Antibody Treatment.

In 2023, the Food and Drug Administration approved 2 new products to reduce the risk of lower respiratory infections caused by respiratory syncytial virus (RSV) in infants: Beyfortus (nirsevimab; AstraZeneca/Sanofi), a single-dose monoclonal antibody for infant administration, and Abrysvo (bivalent RSVpreF vaccine; Pfizer), a single-dose maternal vaccination. We aimed to synthesize data from the literature and the leading professional organizations to provide guidance on RSV and strategies to reduce the risk of infant infection. This information will assist prenatal care clinicians in counseling their patients regarding the choice between maternal vaccination and the infant monoclonal antibody. A descriptive review of the guidelines from the Centers for Disease Control and Prevention, American College of Obstetrics and Gynecology (ACOG), American Academy of Pediatrics, Society for Maternal-Fetal Medicine, and the American Academy of Family Physicians. All 5 organizations recommend that RSV vaccination should be offered to all pregnant people during the RSV season (September-January in the continental United States). Infants younger than 8 months entering into their first RSV season born to those who did not receive maternal vaccination or received vaccination less than 14 days prior to birth should be offered monoclonal antibody administration. RSV vaccination and monoclonal antibodies have the potential to significantly reduce the burden of lower respiratory tract infections due to RSV in infants. Future studies should further evaluate the durability of protection and other strategies to further protect the infant, including cocooning and the role of breast milk in immunity.

Preventing respiratory syncytial virus in infants.

Preventing respiratory syncytial virus in infants.

Use of the Abrysvo Vaccine in Pregnancy to Prevent Respiratory Syncytial Virus in Infants: A Review.

The FDA's approval of Pfizer's new respiratory syncytial virus (RSV) prefusion (preF) vaccine, Abrysvo, marks a critical milestone in infant health and well-being by preventing lower respiratory tract infections in the most vulnerable. The vaccine has been approved for administration to pregnant women at 32 to 36 weeks of gestation and elderly people over 60. This review explores the Abrysvo vaccine, detailing its mechanism, efficacy, safety, and adverse events. It aims to inform healthcare providers about this vital method for safeguarding infant respiratory health through maternal immunization.

Assessment of effectiveness and impact of universal prophylaxis with nirsevimab for prevention of hospitalizations due to respiratory syncytial virus in infants. The NIRSE-GAL study protocol

ABSTRACT Nirsevimab has been recently licensed for universal RSV prophylaxis in infants. NIRSE-GAL is a three-year population-based study initiated in Galicia in September 2023. It aims to evaluate nirsevimab effectiveness against RSV-related hospitalizations lower respiratory tract infections (LRTI), severe RSV, all-cause LRTI, and all-cause hospitalization. NIRSE-GAL also aims to estimate nirsevimab impact on primary healthcare use in the short and mid-term, children’s wheezing and asthma, and medical prescriptions for RSV. The immunization campaigns will be scheduled based on the expected start week for the RSV season and will last the whole season. Immunization will be offered to: i) infants born during the campaign (seasonal), ii) infants < 6 months at the start of the campaign (catch-up), and iii) infants with high-risk factors, aged 6–24 months at the start of the campaign (high-risk). The follow-up period will start: i) the immunization date for all immunized infants, ii) the start of the campaign, for the non-immunized catch-up or high-risk groups, or iii) the birthdate for the non-immunized seasonal group. Infants will be followed up until outcome occurrence, death, or end of study. Nirsevimab effectiveness will be estimated using Poisson and Cox regression models. Sensitivity and stratified analyses will be undertaken. The number of averted cases and the number needed to immunize will be estimated. Immunization failure and nirsevimab safety will be monitored. NIRSE-GAL was approved by the ethics committee of Galicia (CEIC 2023–377) and registered in ClinicalTrials.gov (ID: NCT06180993). Findings will be mainly shared via peer-reviewed publications and scientific conferences.

Assessing the Real-World Effectiveness of Immunizations for Respiratory Syncytial Virus

This Viewpoint discusses recommendations from the US Centers for Disease Control and Prevention for newly licensed immunizations for respiratory syncytial virus in infants, children with high-risk conditions, and older adults.

Burden of disease of respiratory syncytial virus in infants, young children and pregnant women and people.

Passive immunization products for infants and pregnant women and people have sparked interest in understanding Canada's respiratory syncytial virus (RSV) burden. This rapid review examines RSV burden of disease in infants, young children and pregnant women and people. Electronic databases were searched to identify studies and systematic reviews reporting data on outpatient visits, hospitalizations, intensive care unit admissions, deaths and preterm labour associated with RSV. We also contacted Canadian respiratory virus surveillance experts for additional data. Overall, 17 studies on infants and young children and 10 studies on pregnant women and people were included, in addition to primary surveillance data from one Canadian territory (Yukon). There were higher rates of medical utilization for infants than older children. Hospitalization rates were highest in infants under six months (more than 1% annually), with 5% needing intensive care unit admission, but mortality was low. Severe outcomes often occurred in healthy full-term infants and burden was higher than influenza. Respiratory syncytial virus attack rate was 10%-13% among pregnant women and people. Only one study found a higher hospitalization rate in pregnant women and people compared to non-pregnant women and people. Limited evidence was found on intensive care unit admission, death and preterm birth for pregnant women and people. While risk of severe outcomes is larger in high-risk infants and children, healthcare burden is greatest in healthy term infants. The RSV severity for pregnant women and people appears to be similar to that for non-pregnant women and people.

Parental awareness and attitudes towards prevention of respiratory syncytial virus in infants and young children in Australia.

To assess parental awareness of respiratory syncytial virus (RSV) and the level of acceptance of future RSV prevention strategies. A cross-sectional online survey was implemented targeting "future" and "current" parents of children aged ≤5 years in Australia. From 1992 eligible participants, two non-mutually exclusive subgroups were formed: "current" parents (N = 1931) and "pregnant/planning" parents (N = 464: 403 also "current" parents and 61 "future" parents). Participants were predominantly (86.6%) aged 25-39 years and 68.5% with university education. The majority (89.6% current; 78.7% future) had heard of RSV. Of those, 64.2% (current) and 50.0% (future) were aware that pneumonia is associated with RSV; 71.8% (current) and 52.1% (future) were aware that bronchiolitis is associated with RSV. In multivariable logistic regression analyses, Australian-born parents (aOR = 2.47 [95% CI: 1.48-4.12]), living in the eastern states (e.g., New South Wales: aOR = 6.15 [95% CI:2.10-18.04]), with a university-level education (aOR = 2.61 [95% CI:1.38-4.94]) and being a current parent (aOR = 12.26 [95% CI:2.82-53.28]) were associated with higher RSV awareness. There was a high level of acceptance for maternal vaccines (future: 79.3%) and infant immunisation (all: 81.7%). While RSV awareness and immunisation acceptance were high, there was limited knowledge of severity of RSV, especially in future parents. Education campaigns need to be developed to increase RSV knowledge.

Society for Maternal-Fetal Medicine Statement: Clinical considerations for the prevention of respiratory syncytial virus disease in infants

Respiratory syncytial virus is a leading cause of lower respiratory tract illness globally in children under 5 years. Each year, approximately 58,000 hospitalizations in the United States are attributed to respiratory syncytial virus. Infants aged 6 months and younger experience the most severe morbidity and mortality. Until recently, prevention with the monoclonal antibody, palivizumab, was only offered to infants with high-risk conditions, and treatment primarily consisted of supportive care. Currently, two products are approved for the prevention of respiratory syncytial virus in infants. These include the Pfizer bivalent recombinant respiratory syncytial virus prefusion F protein subunit vaccine, administered seasonally to the pregnant person between 32 0/7 and 36 6/7 weeks of gestation, and the monoclonal antibody, nirsevimab, administered to infants up to 8 months entering their first respiratory syncytial virus season. With few exceptions, administering both the vaccine to the pregnant person and monoclonal antibody to the infant is not recommended. All infants should be protected against respiratory syncytial virus using one of these strategies. Key considerations for pregnant individuals include examining available safety and efficacy data, weighing accessibility and availability, and patient preferences for maternal vaccination versus infant monoclonal antibody treatment. It will be critical for maternal-fetal medicine physicians to provide effective and balanced counseling to aid patients in deciding on a personalized approach to the prevention of respiratory syncytial virus in their infants.

Cost-Effectiveness of Nirsevimab for the Prevention of Respiratory Syncytial Virus Infection in Infants

&#x0D; During CADTH’s search of the economic literature, 3 economic studies were identified that assessed the cost-effectiveness of a long-acting monoclonal antibody, nirsevimab, as an intervention to prevent respiratory syncytial virus in infants in high-income countries, including 1 study set in Nunavik.&#x0D; The 3 studies were conducted for different geographical locations: Canada, the US, and England and Wales. While each study conducted an economic evaluation, their approaches differed: 1 was a cost-consequence analysis and the other 2 were cost-utility analyses.&#x0D; The results from the 3 studies varied considerably, and the nirsevimab programs differed (e.g., in terms of patients eligible for immunization). In general, nirsevimab was generally more effective and associated with lower total costs than comparator programs. The results were sensitive to the modelled region, source of efficacy data, price of nirsevimab, and severity of the respiratory syncytial virus season.&#x0D; The generalizability of the identified studies to Canadian policy-making may be limited given the population compositions and cost parameters included in the models. To understand the potential cost-effectiveness of nirsevimab, a de novo economic evaluation would be required that compared nirsevimab with the existing preventive strategies employed in Canada (which may include monoclonal antibodies for infants) and is conducted in a Canadian setting.&#x0D;

The disease burden of respiratory syncytial virus in Infants.

To describe the current global burden of respiratory syncytial virus (RSV) in infants and its implications for morbidity, health resources and economic costs. New prophylactic therapies are on the horizon for RSV in the form of long-acting monoclonal antibodies suitable for healthy infants and maternal immunizations. Despite being responsible for significant global infant morbidity and mortality, until recently there have been no effective therapeutics available for healthy infants to protect them from RSV. Several new drugs are likely to be available within the next few years which could help relieve a huge burden on healthcare systems over the coming winters.

Breastfeeding and respiratory syncytial virus

George Winter looks at recent research into the impact breastfeeding can have on the prevention of severe respiratory syncytial virus in infants

Monoclonal Antibody for the Prevention of Respiratory Syncytial Virus in Infants and Children

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infection in children younger than 5 years; effective prevention strategies are urgently needed. To compare the efficacy and safety of monoclonal antibodies for the prevention of RSV infection in infants and children. In this systematic review and network meta-analysis, PubMed, Embase, CENTRAL, and ClinicalTrials.gov were searched from database inception to March 2022. Randomized clinical trials that enrolled infants at high risk of RSV infection to receive a monoclonal antibody or placebo were included. Keywords and extensive vocabulary related to monoclonal antibodies, RSV, and randomized clinical trials were searched. The Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guideline was used. Teams of 2 reviewers independently performed literature screening, data extraction, and risk of bias assessment. The Grading of Recommendations, Assessments, Developments, and Evaluation approach was used to rate the certainty of evidence. A random-effects model network meta-analysis was conducted using a consistency model under the frequentist framework. The main outcomes were all-cause mortality, RSV-related hospitalization, RSV-related infection, drug-related adverse events, intensive care unit admission, supplemental oxygen use, and mechanical ventilation use. Fifteen randomized clinical trials involving 18 395 participants were eligible; 14 were synthesized, with 18 042 total participants (median age at study entry, 3.99 months [IQR, 3.25-6.58 months]; median proportion of males, 52.37% [IQR, 50.49%-53.85%]). Compared with placebo, with moderate- to high-certainty evidence, nirsevimab, palivizumab, and motavizumab were associated with significantly reduced RSV-related infections per 1000 participants (nirsevimab: -123 [95% CI, -138 to -100]; palivizumab: -108 [95% CI, -127 to -82]; motavizumab: -136 [95% CI, -146 to -125]) and RSV-related hospitalizations per 1000 participants (nirsevimab: -54 [95% CI, -64 to -38; palivizumab: -39 [95% CI, -48 to -28]; motavizumab: -48 [95% CI, -58 to -33]). With moderate-certainty evidence, both motavizumab and palivizumab were associated with significant reductions in intensive care unit admissions per 1000 participants (-8 [95% CI, -9 to -4] and -5 [95% CI, -7 to 0], respectively) and supplemental oxygen use per 1000 participants (-59 [95% CI, -63 to -54] and -55 [95% CI, -61 to -41], respectively), and nirsevimab was associated with significantly reduced supplemental oxygen use per 1000 participants (-59 [95% CI, -65 to -40]). No significant differences were found in all-cause mortality and drug-related adverse events. Suptavumab did not show any significant benefits for the outcomes of interest. In this study, motavizumab, nirsevimab, and palivizumab were associated with substantial benefits in the prevention of RSV infection, without a significant increase in adverse events compared with placebo. However, more research is needed to confirm the present conclusions, especially for safety and cost-effectiveness.

Assessment of the Programmatic Suitability and User Acceptability of Delivery Devices for the Prevention of Respiratory Syncytial Virus in Infants

Assessment of the Programmatic Suitability and User Acceptability of Delivery Devices for the Prevention of Respiratory Syncytial Virus in Infants

Molecular Detection of Respiratory Syncytial Virus in Infants and Young Children by the Conventional Reverse Transcriptase Polymerase Chain Reaction

Molecular Detection of Respiratory Syncytial Virus in Infants and Young Children by the Conventional Reverse Transcriptase Polymerase Chain Reaction

IRIS: Infection with RespIratory Syncytial Virus in infants—a prospective observational cohort study

BackgroundRespiratory syncytial virus (RSV) is the most common cause of acute lower respiratory tract infection in infants. Globally, RSV is responsible for approximately 3.2 million hospital admissions and about 60,000 in-hospital deaths per year.MethodsInfection with RespIratory Syncytial Virus (IRIS) is an observational, multi-centre study enrolling infants with severe RSV infection and healthy controls. Inclusion criteria are age between 0 and 36 months and hospitalisation due to RSV infection at three German sites. Exclusion criteria are premature birth, congenital or acquired bronchopulmonary or cardiac diseases, and immunodeficiency. Healthy control probands are enrolled via recruitment of patients undergoing routine surgical procedures. Blood and respiratory specimens are collected upon admission, and RSV and other pathogens are analysed by multiplex polymerase chain reaction. Different biomaterials, including plasma, nasal lining fluid, blood cells, DNA, and RNA specimens, are sampled in a dedicated biobank. Detailed information on demographic characteristics and medical history is recorded, and comprehensive clinical data, including vital signs, medication, and interventions.DiscussionThe IRIS study aims to discover host and viral factors controlling RSV disease courses in infants. The approach including multi-omics characterisation in clinically well-characterized children with RSV bronchiolitis seeks to improve our understanding of the immune response against this virus. It may disclose novel diagnostic and treatment approaches for respiratory infections in infants.Trial registration: ClinicalTrials.gov, NCT04925310. Registered 01 October 2021—Retrospectively registered. https://clinicaltrials.gov/ct2/show/NCT04925310?cond=NCT04925310&draw=2&rank=1

Comparison of clinical presentations and burden of respiratory syncytial virus in infants across three distinct healthcare settings in Davidson County, Tennessee.

Background:The burden of respiratory syncytial virus (RSV)-associated acute respiratory illnesses among healthy infants (<1 year) in the inpatient setting is well established. The focus on RSV-associated illnesses in the outpatient (OP) and emergency department (ED) settings are however understudied. We sought to determine the spectrum of RSV illnesses in infants at three distinct healthcare settings.Methods:From 16 December 2019 through 30 April 2020, we performed an active, prospective RSV surveillance study among infants seeking medical attention from an inpatient (IP), ED, or OP clinic. Infants were eligible if they presented with fever and/or respiratory symptoms. Demographics, clinical characteristics, and illness histories were collected during parental/guardian interviews, followed by a medical chart review and illness follow-up surveys. Research nasal swabs were collected and tested for respiratory pathogens for all enrolled infants.Results:Of the 627 infants screened, 475 were confirmed eligible; 360 were enrolled and research tested. Within this final cohort, 101 (28%) were RSV-positive (IP = 37, ED = 18, and OP = 46). Of the RSV-positive infants, the median age was 4.5 months and 57% had ⩾2 healthcare encounters. The majority of RSV-positive infants were not born premature (88%) nor had underlying medical conditions (92%). RSV-positive infants, however, were more likely to have a lower respiratory tract infection than RSV-negative infants (76% vs 39%, p < 0.001). Hospitalized infants with RSV were younger, 65% required supplemental oxygen, were more likely to have lower respiratory tract symptoms, and more often had shortness of breath and rales/rhonchi than RSV-positive infants in the ED and OP setting.Conclusion:Infants with RSV illnesses seek healthcare for multiple encounters in various settings and have clinical difference across settings. Prevention measures, especially targeted toward healthy, young infants are needed to effectively reduce RSV-associated healthcare visits.

1406. Comparison of Clinical Presentations and Burden of Respiratory Syncytial Virus in Infants Across Three Distinct Healthcare Settings

BackgroundRespiratory syncytial virus (RSV) accounts for the majority of lower respiratory tract illnesses in hospitalized infants. In the U.S., RSV hospitalizations are well characterized; yet, emergency department (ED) and outpatient (OP) visits are underrecognized. We evaluated the burden of RSV across three distinct healthcare settings during one respiratory season.MethodsFrom 12/16/19-4/30/20, we conducted a prospective RSV surveillance study among Davidson County, TN infants under one year who presented to an inpatient (IP), ED, or one of four OP clinics with either fever or any upper respiratory (i.e., cough, earache, nasal congestion, rhinorrhea, sore throat) and/or lower respiratory [i.e., wheezing, crackles, rales, diminished breath sounds, shortness of breath (SOB)] symptoms. Demographic and illness history were collected during parental/guardian interviews, followed by medical chart abstraction. Nasal swabs were collected and tested for RSV using Luminex® NxTAG RPP. Due to the COVID-19 pandemic, on 3/16/20 enrollment at three of the four OP clinics ceased.ResultsA total of 627 infants were screened, of whom 473 (75%) were confirmed eligible, 364 (77%) enrolled, 361 (99%) were tested for RSV of which 101 (28%) were RSV+ (IP=37, ED=18, OP=46) (Figure 1). Compared to RSV-negative subjects, RSV+ subjects were younger (6.6 vs. 4.9 months, p< 0.001), 56% were male and 48% white. By setting, infants in the OP setting were older than those seen in the IP and ED [(p=0.002), Figure 2]. Compared to infants in the OP setting, hospitalized infants were more likely to present with SOB and rhonchi/rales, but less likely to have only upper respiratory symptoms (Figure 3) and be African American (p=0.046). Infants in the IP setting had a higher proportion of clinical RSV diagnostic testing (73%) compared to the ED (39%) and OP (28%) settings (p< 0.001).Figure 1. Davidson County Infants with RSV by MMWR Week and Healthcare Setting (n=101) Figure 2. Cumulative Enrollment of Davidson County Infants with RSV by Age in Months and Healthcare Setting (n=101) Figure 3. Proportion of Davidson County Infants with RSV Showing each Clinical Symptom, by Healthcare Setting ConclusionTwo-thirds of RSV+ infants sought care from either an OP or ED setting, with nearly all hospitalized infants presenting with both upper and lower respiratory symptoms. The underutilization of diagnostic testing in the OP settings may underestimate the true burden of RSV. Future studies are essential to document the true prevalence of RSV in order to assess the need and impact of new interventions (e.g., immunizations, antivirals).Disclosures Danielle A. Rankin, MPH, CIC, Sanofi Pasteur (Grant/Research Support, Research Grant or Support) Zaid Haddadin, MD, CDC (Grant/Research Support, Research Grant or Support)Quidel Corporation (Grant/Research Support, Research Grant or Support)sanofi pasteur (Grant/Research Support, Research Grant or Support) Jon Fryzek, PhD, MPH, EpidStrategies (Employee) Mina Suh, MPH, International Health, EpidStrategies (Employee) Donald S. Shepard, PhD, Sanofi Pasteur (Grant/Research Support) Natasha B. Halasa, MD, MPH, Genentech (Other Financial or Material Support, I receive an honorarium for lectures - it’s a education grant, supported by genetech)Karius (Consultant)Moderna (Consultant)Quidel (Grant/Research Support, Research Grant or Support)Sanofi (Grant/Research Support, Research Grant or Support)

Cost-analysis of Withdrawing Immunoprophylaxis for Respiratory Syncytial Virus in Infants Born at 33–35 Weeks Gestational Age in Quebec

In 2015, the Quebec Ministry of Health limited palivizumab prophylaxis for respiratory syncytial virus (RSV) in premature infants to those born at <33 weeks gestational age (wGA), unless other indications were present. We compared RSV-related costs for 2 seasons before the change (2013-2014, 2014-2015) and 2 seasons after (2015-2016, 2016-2017) in premature infants 33-35 wGA. Using payer and societal perspectives, costs associated with hospitalizations for RSV and lower respiratory tract infection (LRTI) in infants born at 33-35 wGA were estimated. Inputs were from a 2013-2017 retrospective cohort study in 25 Quebec hospitals of RSV/LRTI hospitalizations among infants <6 months old at the start of, or born during, the RSV season. Resource utilization data (hospital stay, procedures, visits, transportation, out-of-pocket expenses and work productivity) were collected from charts and parent interviews allowing estimation of direct and indirect costs. Costs, including palivizumab administration, were derived from provincial sources and adjusted to 2018 Canadian dollars. Costs were modeled for preterm infants hospitalized for RSV/LRTI pre- and postrevision of guidelines and with matched term infants hospitalized for RSV/LRTI during 2015-2017 (comparator). Average total direct and indirect costs for 33-35 wGA infants were higher postrevision of guidelines ($29,208/patient, 2015-2017; n = 130) compared with prerevision ($16,976/patient, 2013-2015; n = 105). Total costs were higher in preterm infants compared with term infants (n = 234) postrevision of guidelines ($29,208/patient vs. $10,291/patient). Immunoprophylaxis for RSV in infants born at 33-35 wGA held a cost advantage for hospitalizations due to RSV/LRTI.

Underdetection of laboratory-confirmed influenza-associated hospital admissions among infants: a multicentre, prospective study

Since influenza often presents non-specifically in infancy, we aimed to assess the extent to which existing respiratory surveillance platforms might underestimate the frequency of severe influenza disease among infants. The Influenza and Respiratory Syncytial Virus in Infants (IRIS) study was a prospective observational study done at four hospitals in Albania, Jordan, Nicaragua, and the Philippines. We included acutely ill infants aged younger than 1 year admitted to hospital within 10 days or less of illness onset during two influenza seasons (2015-16 and 2016-17) in Albania, Jordan, and Nicaragua, and over a continuous 34 week period (2015-16) in the Philippines. We assessed the frequency of influenza virus infections by real-time RT-PCR (rRT-PCR) and serology. The main study outcome was seroconversion, defined as convalescent antibody titres more than or equal to four-fold higher than acute sera antibody titres, and convalescent antibody titres of 40 or higher. Seroconverison was confirmed by haemagglutination inhibition assay for influenza A viruses, and by hemagglutination inhibition assay and microneutralisation for influenza B viruses. Between June 27, 2015, and April 21, 2017, 3634 acutely ill infants were enrolled, of whom 1943 were enrolled during influenza seasons and had complete acute-convalescent pairs and thus were included in the final analytical sample. Of the 1943 infants, 94 (5%) were influenza-positive by both rRT-PCR and serology, 58 (3%) were positive by rRT-PCR-only, and 102 (5%) were positive by serology only. Seroconversion to at least one of the influenza A or B viruses was observed among 196 (77%) of 254 influenza-positive infants. Of the 254 infants with influenza virus, 84 (33%) only had non-respiratory clinical discharge diagnoses (eg, sepsis, febrile seizures, dehydration, or other non-respiratory viral illness). A focus on respiratory diagnoses and rRT-PCR-confirmed influenza underdetects influenza-associated hospital admissions among infants by a factor of 2·6 (95% CI 2·0-3·6). Findings were unchanged when syndromic severe acute respiratory infection criteria were applied instead of clinical diagnosis. If the true incidence of laboratory-confirmed influenza-associated hospital admissions among infants is at least twice that of previous estimates, this substantially increases the global burden of severe influenza and expands our estimates of the preventive value of maternal and infant influenza vaccination programmes. US Centers for Disease Control and Prevention.

Haemophilus-Dominant Nasopharyngeal Microbiota Is Associated With Delayed Clearance of Respiratory Syncytial Virus in Infants Hospitalized for Bronchiolitis.

The relation of nasopharyngeal microbiota to the clearance of respiratory syncytial virus (RSV) in infants hospitalized for bronchiolitis is not known. In a multicenter cohort, we found that 106 of 557 infants (19%) hospitalized with RSV bronchiolitis had the same RSV subtype 3 weeks later (ie, delayed clearance of RSV). Using 16S ribosomal RNA gene sequencing and a clustering approach, infants with a Haemophilus-dominant microbiota profile at hospitalization were more likely than those with a mixed profile to have delayed clearance, after adjustment for 11 factors, including viral load. Nasopharyngeal microbiota composition is associated with delayed RSV clearance.