The resurgence of influenza A/H3N2 virus in Australia after the relaxation of COVID-19 restrictions during the 2022 season.

This study retrospectively analyzed the genetic characteristics of influenza A H3N2 (A/H3N2) viruses circulating in New South Wales (NSW), the Australian state with the highest number of influenza cases in 2022, and explored the phylodynamics of A/H3N2 transmission within Australia during this period. Sequencing was performed on 217 archived specimens, and A/H3N2 evolution and spread within Australia were analyzed using phylogenetic and phylodynamic methods. Hemagglutinin genes of all analyzed NSW viruses belonged to subclade 3C.2a1b.2a.2 and clustered together with the 2022 vaccine strain. Complete genome analysis of NSW viruses revealed highly frequent interclade reassortments between subclades 3C.2a1b.2a.2 and 3C.2a1b.1a. The estimated earliest introduction time of the dominant subgroup 3C.2a1b.2a.2a.1 in Australia was February 22, 2022 (95% highest posterior density: December 19, 2021-March 13, 2022), following the easing of Australian travel restrictions, suggesting a possible international source. Phylogeographic analysis revealed that Victoria drove the transmission of A/H3N2 viruses across the country during this season, while NSW did not have a dominant role in viral dissemination to other regions. This study highlights the importance of continuous surveillance and genomic characterization of influenza viruses in the postpandemic era, which can inform public health decision-making and enable early detection of novel strains with pandemic potential.

Machine Learning Color Feature Analysis of a High Throughput Nanoparticle Conjugate Sensing Assay.

Plasmonic nanoparticles are finding applications within the single molecule sensing field in a "dimer" format, where interaction of the target with hairpin DNA causes a decrease in the interparticle distance, leading to a localized surface plasmon resonance shift. While this shift may be detected using spectroscopy, achieving statistical relevance requires the measurement of thousands of nanoparticle dimers and the timescales required for spectroscopic analysis are incompatible with point-of-care devices. However, using dark-field imaging of the dimer structures, simultaneous digital analysis of the plasmonic resonance shift after target interaction of thousands of dimer structures may be achieved in minutes. The main challenge of this digital analysis on the single-molecule scale was the occurrence of false signals caused by non-specifically bound clusters of nanoparticles. This effect may be reduced by digitally separating dimers from other nanoconjugate types. Variation in image intensity was observed to have a discernible impact on the color analysis of the nanoconjugate constructs and thus the accuracy of the digital separation. Color spaces wherein intensity may be uncoupled from the color information (hue, saturation, and value (HSV) and luminance, a* vector, and b* vector (LAB) were contrasted to a color space which cannot uncouple intensity (RGB) to train a classifier algorithm. Each classifier algorithm was validated to determine which color space produced the most accurate digital separation of the nanoconjugate types. The LAB-based learning classifier demonstrated the highest accuracy for digitally separating nanoparticles. Using this classifier, nanoparticle conjugates were monitored for their plasmonic color shift after interaction with a synthetic RNA target, resulting in a platform with a highly accurate yes/no response with a true positive rate of 88% and a true negative rate of 100%. The sensor response of tested single stranded RNA (ssRNA) samples was well above control responses for target concentrations in the range of 10 aM-1 pM.

Detection of respiratory viruses directly from clinical samples using next-generation sequencing: A literature review of recent advances and potential for routine clinical use.

Acute respiratory infection is the third most frequent cause of mortality worldwide, causing over 4.25 million deaths annually. Although most diagnosed acute respiratory infections are thought to be of viral origin, the aetiology often remains unclear. The advent of next-generation sequencing (NGS) has revolutionised the field of virus discovery and identification, particularly in the detection of unknown respiratory viruses. We systematically reviewed the application of NGS technologies for detecting respiratory viruses from clinical samples and outline potential barriers to the routine clinical introduction of NGS. The five databases searched for studies published in English from 01 January 2010 to 01 February 2021, which led to the inclusion of 52 studies. A total of 14 different models of NGS platforms were summarised from included studies. Among these models, second-generation sequencing platforms (e.g., Illumina sequencers) were used in the majority of studies (41/52, 79%). Moreover, NGS platforms have proven successful in detecting a variety of respiratory viruses, including influenza A/B viruses (9/52, 17%), SARS-CoV-2 (21/52, 40%), parainfluenza virus (3/52, 6%), respiratory syncytial virus (1/52, 2%), human metapneumovirus (2/52, 4%), or a viral panel including other respiratory viruses (16/52, 31%). The review of NGS technologies used in previous studies indicates the advantages of NGS technologies in novel virus detection, virus typing, mutation identification, and infection cluster assessment. Although there remain some technical and ethical challenges associated with NGS use in clinical laboratories, NGS is a promising future tool to improve understanding of respiratory viruses and provide a more accurate diagnosis with simultaneous virus characterisation.

Viruses associated with acute respiratory infection in a community-based cohort of healthy New Zealand children.

Acute respiratory infections (ARIs) are a major cause of morbidity among children. Respiratory viruses are commonly detected in both symptomatic and asymptomatic periods. The rates of infection and community epidemiology of respiratory viruses in healthy children needs further definition to assist interpretation of molecular diagnostic assays in this population. Children otherwise healthy aged 1 to 8 years were prospectively enrolled in the study during two consecutive winters, when ARIs peak in New Zealand. Parents completed a daily symptom diary for 8 weeks, during which time they collected a nasal swab from the child for each clinical ARI episode. A further nasal swab was collected by research staff during a clinic visit at the conclusion of the study. All samples were tested for 15 respiratory viruses commonly causing ARI using molecular multiplex polymerase chain reaction assays. There were 575 ARIs identified from 301 children completing the study, at a rate of 1.04 per child-month. Swabs collected during an ARI were positive for a respiratory virus in 76.8% (307 of 400), compared with 37.3% (79 of 212) of swabs collected during asymptomatic periods. The most common viruses detected were human rhinovirus, coronavirus, parainfluenza viruses, influenzavirus, respiratory syncytial virus, and human metapneumovirus. All of these were significantly more likely to be detected during ARIs than asymptomatic periods. Parent-administered surveillance is a useful mechanism for understanding infectious disease in healthy children in the community. Interpretation of molecular diagnostic assays for viruses must be informed by understanding of local rates of asymptomatic infection by such viruses.

Transplacental transfer of RSV antibody in Australian First Nations infants.

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory infection hospitalisations in Aboriginal infants specifically those aged <6 months. Maternally derived RSV antibody (Ab) can protect against severe RSV disease in infancy. However, the efficiency of transplacental transfer of maternal anti-RSV Ab remains unknown in Aboriginal infants. We characterised RSV Ab in Australian First Nations mother-infant pairs (n = 78). We investigated impact of covariates including low birthweight, gestational age (GA), sex of the baby, maternal age and multiparity of the mother on cord to maternal anti-RSV Ab titre ratio (CMTR) using multivariable logistic regression model. All (n = 78) but one infant was born full term (median GA: 39 weeks, interquartile range: 38-40 weeks) and 56% were males. The mean log2 RSV Ab titre was 10.7 (SD± 1.3) in maternal serum and 11.0 (SD ± 1.3) in cord serum at birth; a ratio of 1.02 (SD ± 0.06). One-third of the pairs had a CMTR of <1 indicating impaired transfer. Almost 9% (7/78) of the term infants had cord RSV Ab levels below

Global epidemiology of nonpolio enteroviruses causing severe neurological complications: A systematic review and meta-analysis.

Enteroviruses are RNA viruses found as commensals in the human gut and respiratory system, which may cause a wide spectrum of disease. Enteroviruses may cause severe neurologic complications including acute flaccid paralysis (AFP) and encephalitis and are the most commonly diagnosed agents of viral meningitis. Outbreaks of more severe disease are often associated with particular genotypes, such as enterovirus-A71 causing rhombencephalitis and AFP. There are more than 300 described genotypes of human enterovirus, with overlaps in clinical phenotypes between genotypes, and uncertainty about which genotypes are more prevalent in neurological manifestations. A systematic review of observational studies was conducted to evaluate the most prevalent enterovirus genotypes causing AFP, encephalitis, and meningitis. The genotyping methods and sampling sites were compiled as secondary outcomes. Sources included MEDLINE, Embase (publications until January 2019), and references selected from included studies. Meta-analyses using a random effects model were performed to calculate the pooled proportion of enterovirus genotypes in each disease. Ninety-six publications met the eligibility criteria, comprising 3779 AFP cases, 1140 encephalitis cases, and 32 810 meningitis cases. Enterovirus-A71 was most frequently associated with AFP (pooled proportion 0.12, 95% CI, 0.05-0.20) and encephalitis (0.77, 95% CI, 0.61-0.91). Echovirus 30 (0.35, 95% CI, 0.27-0.42) was the most predominant genotype in meningitis cases. Genotypes were most commonly determined using VP1 RT- reverse transcription-polymerase chain reaction, and most samples assessed were cerebrospinal fluid. With the emergence of enteroviruses as an increasing cause of neurological diseases, surveillance and testing need to increase to identify the aetiology of the most common and most severe disorders.

SARS-CoV-2 in human milk is inactivated by Holder pasteurisation but not cold storage.

AIM: As the COVID-19 pandemic evolves, human milk banks world-wide continue to provide donor human milk to vulnerable infants who lack access to mother's own milk. Under these circumstances, ensuring the safety of donor human milk is paramount, as the risk of vertical transmission of SARS-CoV-2 is not fully understood. Here, we investigate the inactivation of SARS-CoV-2 in human milk by pasteurisation and the stability of SARS-CoV-2 in human milk under cold storage. METHODS: SARS-CoV-2 was experimentally inoculated into human milk samples from healthy donors or into a control medium. Triplicates of each sample were layered onto uninfected cells after Holder pasteurisation (63°C for 30 min), heating to 56°C for 30 min, or after 48 h of storage at 4°C or -30°C. Infectious titres of virus were determined at 72 h post-infection by endpoint titration. RESULTS: Following heating to 63°C or 56°C for 30 min, replication competent (i.e. live) SARS-CoV-2 was undetected in both human milk and the control medium. Cold storage of SARS-CoV-2 in human milk (either at 4°C or -30°C) did not significantly impact infectious viral load over a 48 h period. CONCLUSION: SARS-CoV-2 is effectively inactivated by Holder pasteurisation, suggesting that existing milk bank processes will effectively mitigate the risk of transmission of SARS-COV-2 to vulnerable infants through pasteurised donor human milk. The demonstrated stability of SARS-CoV-2 in refrigerated or frozen human milk may assist in the development of guidelines around safe expressing and storing of milk from COVID-19 infected mothers.

Systematic review of the impact of point-of-care testing for influenza on the outcomes of patients with acute respiratory tract infection.

Acute respiratory tract infections are a major cause of morbidity and mortality and represent a significant burden on the health care system. Laboratory testing is required to definitively distinguish infecting influenza virus from other pathogens, resulting in prolonged emergency department (ED) visits and unnecessary antibiotic use. Recently available rapid point-of-care tests (POCT) may allow for appropriate use of antiviral and antibiotic treatments and decrease patient lengths of stay. We undertook a systematic review to assess the effect of POCT for influenza on three outcomes: (1) antiviral prescription, (2) antibiotic prescription, and (3) patient length of stay in the ED. The databases Medline and Embase were searched using MeSH terms and keywords for influenza, POCT, antivirals, antibiotics, and length of stay. Amongst 245 studies screened, 30 were included. The majority of papers reporting on antiviral prescription found that a positive POCT result significantly increased use of antivirals for influenza compared with negative POCT results and standard supportive care. A positive POCT result also led to decreased antibiotic use. The results of studies assessing the effect of POCT on ED length of stay were not definitive. The studies assessed in this systematic review support the use of POCT for diagnosis of influenza in patients suffering an acute respiratory infection. Diagnosis using POCT may lead to more appropriate prescription of treatments for infectious agents. Further studies are needed to assess the effect of POCT on the length of stay in ED.

Contamination by respiratory viruses on outer surface of medical masks used by hospital healthcare workers.

BACKGROUND: Medical masks are commonly used in health care settings to protect healthcare workers (HCWs) from respiratory and other infections. Airborne respiratory pathogens may settle on the surface of used masks layers, resulting in contamination. The main aim of this study was to study the presence of viruses on the surface of medical masks. METHODS: Two pilot studies in laboratory and clinical settings were carried out to determine the areas of masks likely to contain maximum viral particles. A laboratory study using a mannequin and fluorescent spray showed maximum particles concentrated on upper right, middle and left sections of the medical masks. These findings were confirmed through a small clinical study. The main study was then conducted in high-risk wards of three selected hospitals in Beijing China. Participants (n = 148) were asked to wear medical masks for a shift (6-8 h) or as long as they could tolerate. Used samples of medical masks were tested for presence of respiratory viruses in upper sections of the medical masks, in line with the pilot studies. RESULTS: Overall virus positivity rate was 10.1% (15/148). Commonly isolated viruses from masks samples were adenovirus (n = 7), bocavirus (n = 2), respiratory syncytial virus (n = 2) and influenza virus (n = 2). Virus positivity was significantly higher in masks samples worn for > 6 h (14.1%, 14/99 versus 1.2%, 1/49, OR 7.9, 95% CI 1.01-61.99) and in samples used by participants who examined > 25 patients per day (16.9%, 12/71 versus 3.9%, 3/77, OR 5.02, 95% CI 1.35-18.60). Most of the participants (83.8%, 124/148) reported at least one problem associated with mask use. Commonly reported problems were pressure on face (16.9%, 25/148), breathing difficulty (12.2%, 18/148), discomfort (9.5% 14/148), trouble communicating with the patient (7.4%, 11/148) and headache (6.1%, 9/148). CONCLUSION: Respiratory pathogens on the outer surface of the used medical masks may result in self-contamination. The risk is higher with longer duration of mask use (> 6 h) and with higher rates of clinical contact. Protocols on duration of mask use should specify a maximum time of continuous use, and should consider guidance in high contact settings. Viruses were isolated from the upper sections of around 10% samples, but other sections of masks may also be contaminated. HCWs should be aware of these risks in order to protect themselves and people around them.

The association between acute flaccid myelitis (AFM) and Enterovirus D68 (EV-D68) - what is the evidence for causation?

BackgroundEnterovirus D68 (EV-D68) has historically been a sporadic disease, causing occasional small outbreaks of generally mild infection. In recent years, there has been evidence of an increase in EV-D68 infections globally. Large outbreaks of EV-D68, with thousands of cases, occurred in the United States, Canada and Europe in 2014. The outbreaks were associated temporally and geographically with an increase in clusters of acute flaccid myelitis (AFM).Aims: We aimed to evaluate a causal association between EV-D68 and AFM. Methods: Using data from the published and grey literature, we applied the Bradford Hill criteria, a set of nine principles applied to examine causality, to evaluate the relationship between EV-D68 and AFM. Based on available evidence, we defined the Bradford Hill Criteria as being not met, or met minimally, partially or fully. Results: Available evidence applied to EV-D68 and AFM showed that six of the Bradford Hill criteria were fully met and two were partially met. The criterion of biological gradient was minimally met. The incidence of EV-D68 infections is increasing world-wide. Phylogenetic epidemiology showed diversification from the original Fermon and Rhyne strains since the year 2000, with evolution of a genetically distinct outbreak strain, clade B1. Clade B1, but not older strains, is associated with AFM and is neuropathic in animal models. Conclusion: While more research is needed on dose-response relationship, application of the Bradford Hill criteria supported a causal relationship between EV-D68 and AFM.

Association of rhinovirus with exacerbations in young children affected by cystic fibrosis: Preliminary data.

Rhinovirus (RV) is a common respiratory viral infection linked to worsening of chronic respiratory diseases including cystic fibrosis (CF) and asthma. RV was tested by RT-PCR in samples (n = 465) collected from the upper (nasal swab, oropharyngeal suction, and sputum) and lower (bronchoalveolar washings) respiratory tract of 110 children with CF. Air samples (n = 52) collected from the operating theatres and outpatient clinics were tested for RV. RV was found in 43% of children <5 years suffering an exacerbation, and 12% of older children (5-17 years). RV particles were detected in the air of clinic rooms. Detection of RV is important in better understanding viral infections in patients with CF.

Outbreak of respiratory syncytial virus (RSV) infection in immunocompromised adults on a hematology ward.

We describe an outbreak of respiratory syncytial virus (RSV) infection on a hematology ward without allogeneic stem cell transplant patients. Twelve patients and one staff member infected with RSV were identified from the laboratory database. Five patients had lower respiratory tract infection, seven had upper respiratory tract infection, one was asymptomatic, and there were two (15.4%) deaths. Most patients had overlapping periods of potential infectiousness on the ward. Sequencing was possible on eight specimens and five of these had identical sequences. Results were consistent with transmission occurring both on the ward and by introduction of RSV from the community. J. Med. Virol. 88:1827-1831, 2016. © 2016 Wiley Periodicals, Inc.

Respiratory syncytial virus is present in the neonatal intensive care unit.

Nosocomial transmission of respiratory syncytial virus (RSV) occurs in children within the neonatal intensive care unit (NICU). During peak community RSV transmission, three swabs were collected from the nose, hand and personal clothing of visitors and health care workers (HCW) in NICU once every week for eight weeks. Nasal swabs were collected from every third neonate and from any neonate clinically suspected of having a respiratory infection. Environmental sampling of high touch areas was done once during the study period. All swabs were tested for RSV using real time RT-PCR. There were 173 (519 total) and 109 (327 total) swabs, each of nose, hand and dress from 84 HCWs and 80 visitors respectively and 81 nasal swabs from 55 neonates collected. Thirty five environmental swabs from surfaces of the beds, side tables, counter tops, chairs, tables and computers were collected. Overall 1% of nasal swabs from each of HCWs, visitors and neonates, 4% of dress specimens from visitors and 9% of environmental swabs were positive for RSV-RNA. The results suggest that though the risk for RSV in the NICU remains low, personnel clothing are contaminated with RSV-RNA and may have a role in transmission.

Absence of back to school peaks in human rhinovirus detections and respiratory symptoms in a cohort of children with asthma.

Much of what is known about the seasonality of human rhinovirus (hRV) infections has been learned from the study of acute asthma exacerbations presenting to emergency care, including those among children at the start of the school term. Much less is known about the patterns of hRVs in the community. In this study, viruses and day-to-day symptoms of asthma and colds were monitored twice weekly in 67 children with asthma aged 5-12 years, over a 15 month period in Sydney, Australia. Overall hRV was detected in 314/1232 (25.5%) of nasal wash samples and 142/1231 (11.5%) of exhaled breath samples; of these, 231 and 24 respectively were genotyped. HRVs were detected with similar prevalence rate throughout the year, including no peak in hRV prevalence following return to school. No peaks were seen in asthma and cold symptoms using twice-weekly diary records. However, over the same period in the community, there were peaks in asthma emergency visits both at a large local hospital and in state-wide hospitalizations, following both return to school (February) and in late autumn (May) in children of the same age. This study suggests that hRV infections are common throughout the year among children, and differences in virus prevalence alone may not account for peaks in asthma symptoms.

Rhinoviruses significantly affect day-to-day respiratory symptoms of children with asthma.

BACKGROUND: Viruses are frequently associated with acute exacerbations of asthma, but the extent to which they contribute to the level of day-to-day symptom control is less clear. OBJECTIVE: We sought to explore the relationship between viral infections, host and environmental factors, and respiratory symptoms in children. METHODS: Sixty-seven asthmatic children collected samples twice weekly for an average of 10 weeks. These included nasal wash fluid and exhaled breath for PCR-based detection of viral RNA, lung function measurements, and records of medication use and asthma and respiratory symptoms in the previous 3 days. Atopy, mite allergen exposure, and vitamin D levels were also measured. Mixed-model regression analyses were performed. RESULTS: Human rhinoviruses (hRVs) were detected in 25.5% of 1232 nasal samples and 11.5% of breath samples. Non-hRV viruses were detected in less than 3% of samples. hRV in nasal samples was associated with asthma symptoms (cough and phlegm: odds ratio = 2.0; 95% CI = 1.4-2.86, P = .0001; wheeze and chest tightness: odds ratio = 2.34, 95% CI = 1.55-3.52, P < .0001) and with cold symptoms, as reported concurrently with sampling and 3 to 4 days later. No differences were found between the 3 hRV genotypes (hRV-A, hRV-B, and hRV-C) in symptom risk. A history of inhaled corticosteroid use, but not atopic status, mite allergen exposure, or vitamin D levels, modified the association between viruses and asthma symptoms. CONCLUSION: The detection of nasal hRV was associated with a significantly increased risk of day-to-day asthma symptoms in children. Host, virus genotype, and environmental factors each had only a small or no effect on the relationship of viral infections to asthma symptoms.

Genome characterization of influenza A and B viruses in New South Wales, Australia, in 2019: A retrospective study using high-throughput whole genome sequencing.

BACKGROUND: During the 2019 severe influenza season, New South Wales (NSW) experienced the highest number of cases in Australia. This study retrospectively investigated the genetic characteristics of influenza viruses circulating in NSW in 2019 and identified genetic markers related to antiviral resistance and potential virulence. METHODS: The complete genomes of influenza A and B viruses were amplified using reverse transcription-polymerase chain reaction (PCR) and sequenced with an Illumina MiSeq platform. RESULTS: When comparing the sequencing data with the vaccine strains and reference sequences, the phylogenetic analysis revealed that most NSW A/H3N2 viruses (n = 68; 94%) belonged to 3C.2a1b and a minority (n = 4; 6%) belonged to 3C.3a. These viruses all diverged from the vaccine strain A/Switzerland/8060/2017. All A/H1N1pdm09 viruses (n = 20) showed genetic dissimilarity from vaccine strain A/Michigan/45/2015, with subclades 6B.1A.5 and 6B.1A.2 identified. All B/Victoria-lineage viruses (n = 21) aligned with clade V1A.3, presenting triple amino acid deletions at positions 162-164 in the hemagglutinin protein, significantly diverging from the vaccine strain B/Colorado/06/2017. Multiple amino acid substitutions were also found in the internal proteins of influenza viruses, some of which have been previously reported in hospitalized influenza patients in Thailand. Notably, the oseltamivir-resistant marker H275Y was present in one immunocompromised patient infected with A/H1N1pdm09 and the resistance-related mutation I222V was detected in another A/H3N2-infected patient. CONCLUSIONS: Considering antigenic drift and the constant evolution of circulating A and B strains, we believe continuous monitoring of influenza viruses in NSW via the high-throughput sequencing approach provides timely and pivotal information for both public health surveillance and clinical treatment.

Acute Q fever in patients with an influenza-like illness in regional New South Wales, Australia.

INTRODUCTION: Query (Q) fever is a zoonosis caused by the bacterium Coxiella burnetii typically presenting as an influenza-like illness (ILI) with or without hepatitis. The infection may be missed by clinicians in settings of low endemicity, as the presentation is clinically not specific, and there are many more common differential diagnoses for ILI including SARS-CoV-2 infection. METHODS: Residual serum samples were retrospectively tested for Phase 1 and 2 Q fever-specific IgM, IgG, IgA antibodies by indirect immunofluorescence and C. burnetii DNA by polymerase chain reaction. They had not been previously tested for Q fever, originating from undiagnosed patients with probable ILI, aged 10-70 years and living in regional New South Wales, Australia. The results were compared with contemperaneous data on acute Q fever diagnostic tests which had been performed based on clinicians requests from a geographically similar population. RESULTS: Only one (0.2%) instance of missed acute Q fever was identified after testing samples from 542 eligible patients who had probable ILI between 2016-2023. Laboratory data showed that during the same period, 731 samples were tested for acute Q fever for clinician-initiated requests and of those 70 (9.6%) were positive. Probability of being diagnosed with Q fever after a clinician initiated request was similar regardless of the patients sex, age and the calendar year of sampling. CONCLUSION: In this sample, Q fever was most likely to be diagnosed via clinician requested testing rather than by testing of undiagnosed patients with an influenza like illness.

Clinical, Genomic, and Immunological Characterization of RSV Surge in Sydney, Australia, 2022.

OBJECTIVES: The 2022 seasonal respiratory syncytial virus (RSV) epidemic in Sydney, Australia saw an unprecedented number of RSV detections. We aimed to characterize genomic and immunologic factors associated with the surge in RSV cases. METHODS: Whole genome sequences of RSV were generated from 264 RSV-infected infants and linked to case-matched clinical data from the 2022 southern hemisphere RSV season. We then performed an immunologic analysis of baseline RSV-specific humoral immunity in women of childbearing age before and throughout the coronavirus disease 2019 pandemic. RESULTS: Clinical analysis revealed a high burden of disease across patients of all health backgrounds. More than one-half of RSV-related health care visits by infants resulted in hospitalization, and one-quarter required high-flow respiratory support or a higher level of care. Viral phylogenetic analyses revealed that 2022 Sydney RSV sequences were closely related to viruses that had been circulating globally since 2017, including those detected in recent US outbreaks. Nonsynonymous mutations within the palivizumab and nirsevimab binding sites were detected at low frequencies. There was no difference in baseline RSV-neutralizing antibody titers between 2020 and 2022. CONCLUSIONS: Collectively, these findings suggest that neither the emergence of a novel RSV genotype nor hypothesized immune debt was associated with the surge of RSV cases and hospitalizations in 2022. Continued genomic and immunologic surveillance is required to further understand the factors driving outbreaks of RSV globally, and to inform guidelines for the rollout and ongoing use of recently developed immunotherapeutics and vaccines.