Level of maternal respiratory syncytial virus (RSV) F antibodies in hospitalized children and correlates of protection

Molecular epidemiology and phylogenetic analysis of human respiratory syncytial virus type B in Riyadh, Saudi Arabia

The human respiratory syncytial virus (HRSV), recently known as the human orthopneumovirus (HOPV), continues to generate new variants with the ability to cause recurrent infections. Data regarding HRSV-B evolution and genetic diversity in Riyadh, Saudi Arabia, are very limited. Therefore, the current study was designed to investigate the prevalence, genetic diversity, and evolution of HRSV-B. A total of 200 nasopharyngeal aspirate (NPA) samples from hospitalized children at King Khaled University Hospital were screened for the presence of HRSV-B. The second hypervariable region (2nd HVR) of the G gene from all 37 HRSV-B genotypes was used to study sequences and family trees. Of the 200 screened nasopharyngeal samples (NPAs), 16 (8%) were positive for HRSV-B, with a high incidence rate in the age group of 2 to 5 months. The analysis of the 2nd HVR region's sequence showed several differences, such as point mutations, different protein lengths, sequence gaps, duplication regions, and glycosylation sites. A total of 46-point mutations were reported, of which 29 changed their corresponding amino acid residues. N-linked glycosylation sites in Riyadh strains were 3, whereas O-linked glycosylation sites ranged from 22 to 32. Phylogenetic analysis revealed that Riyadh strains from the seasons 2019/20 and 2022/23 are grouped into the subclade BA-11. Other Riyadh strains from different previous seasons were clustered into different sub-genotypes (BA-9, -10, and -12). Seasonal surveillance and molecular evolution tracking of HRSV-B is essential for the early detection of viral genotypes that might cause severe illness consequences and widespread transmission.

State of the Art and Emerging Technologies in Vaccine Design for Respiratory Pathogens

In this review, we present the efforts made so far in developing effective solutions to prevent infections caused by seven major respiratory pathogens: influenza virus, respiratory syncytial virus (RSV), the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Bordetella pertussis, Streptococcus pneumoniae (pneumococcus), Mycobacterium tuberculosis, and Pseudomonas aeruginosa. Advancements driven by the recent coronavirus disease 2019 (COVID-19) crisis have largely focused on viruses, but effective prophylactic solutions for bacterial pathogens are also needed, especially in light of the antimicrobial resistance (AMR) phenomenon. Here, we discuss various innovative key technologies that can help address this critical need, such as (a) the development of Lung-on-Chip ex vivo models to gain a better understanding of the pathogenesis process and the host-microbe interactions; (b) a more thorough investigation of the mechanisms behind mucosal immunity as the first line of defense against pathogens; (c) the identification of correlates of protection (CoPs) which, in conjunction with the Reverse Vaccinology 2.0 approach, can push a more rational and targeted design of vaccines. By focusing on these critical areas, we expect substantial progress in the development of new vaccines against respiratory bacterial pathogens, thereby enhancing global health protection in the framework of the increasingly concerning AMR emergence.

Protective or limited? Maternal antibodies and RSV-associated lower respiratory tract infection in hospitalized infants aged 28-90 days

Background

Respiratory syncytial virus (RSV) is a major cause of severe health problems in newborns and young children. The protective role and limitations of serum maternal RSV antibodies in infants under 3 months remain controversial.

Methods

A two-center prospective study from 2020 to 2023 recruited infants (n=286) admitted to the respiratory departments of two children's hospitals in southwestern and southeastern China during RSV epidemic. These infants were hospitalized with lower respiratory tract infections (LRTI). We evaluated the relationship between serum RSV Prefusion (Pre-F), postfusion (Post-F) IgG levels, subtype neutralizing antibodies, and the incidence of RSV infection, as well as the relationship between these maternal antibodies and severity of disease. Since this prospective study only included data from RSV epidemic, we retrospectively reviewed medical records from the Children's Hospital of Chongqing Medical University for the years 2019 to 2023 (n=3467) to analyze population characteristics during both RSV epidemic and non-epidemic periods, using the same inclusion and exclusion criteria.

Result

There were no significant differences in RSV Pre-F IgG, Post-F IgG, or RSV A or B neutralizing antibody levels between the RSV infected and non-infected groups during the epidemic. While RSV Pre-F IgG antibody was inversely correlated with disease severity, RSV Post-F IgG, and RSV A and B neutralizing antibodies did not show a similar correlation across the three illness severity categories. Additionally, there were no differences in age, gender, or illness severity distribution among hospitalized patients during epidemic and non-epidemic periods.

Conclusion

Serum maternal antibody levels offer insufficient protection against RSV-associated LRTI in hospitalized infants aged 28 to 90 days.

Respiratory Syncytial Virus: A WAidid Consensus Document on New Preventive Options

Background/Objectives: Respiratory syncytial virus (RSV) is a leading cause of respiratory infections, particularly affecting young infants, older adults, and individuals with comorbidities. Methods: This document, developed as a consensus by an international group of experts affiliated with the World Association of Infectious Diseases and Immunological Disorders (WAidid), focuses on recent advancements in RSV prevention, highlighting the introduction of monoclonal antibodies (mAbs) and vaccines. Results: Historically, RSV treatment options were limited to supportive care and the monoclonal antibody palivizumab, which required multiple doses. Recent innovations have led to the development of long-acting mAbs, such as nirsevimab, which provide season-long protection with a single dose. Nirsevimab has shown high efficacy in preventing severe RSV-related lower respiratory tract infections (LRTIs) in infants, reducing hospitalizations and ICU admissions. Additionally, new vaccines, such as RSVpreF and RSVpreF3, target older adults and have demonstrated significant efficacy in preventing LRTIs in clinical trials. Maternal vaccination strategies also show promise in providing passive immunity to newborns, protecting them during the most vulnerable early months of life. This document further discusses the global burden of RSV, its economic impact, and the challenges of implementing these preventative strategies in different healthcare settings. Conclusions: The evidence supports the integration of both passive (mAbs) and active (vaccines) immunization approaches as effective tools to mitigate the public health impact of RSV. The combined use of these interventions could substantially reduce RSV-related morbidity and mortality across various age groups and populations, emphasizing the importance of widespread immunization efforts.

Antibody levels against respiratory syncytial virus fusion protein conformations and lack of association with life-threatening infection in previously healthy infants

BACKGROUND

Humoral immune response against the pre-fusion (pre-F) conformation of respiratory syncytial virus (RSV) F protein has been proposed to play a protective role against infection. An RSV pre-F maternal vaccine has been recently approved in several countries to protect young infants against RSV. We aimed to assess serum IgG titers against the pre-F and post-F conformations of RSV F protein and their association with life-threatening RSV disease (LTD) in previously healthy infants.

METHODS

A prospective cohort study including hospitalized infants <12 months with a first RSV infection was conducted during 2017-2019. Patients with LTD required intensive care and mechanical respiratory assistance. RSV pre-F exclusive and post-F antibody responses were determined by post-F competition and non-competition immunoassays, respectively, and neutralizing activity was measured by plaque reduction neutralization test.

RESULTS

Fifty-eight patients were included; the median age was 3.5 months and 41 % were females. Fifteen patients developed LTD. RSV F-specific antibody titers positively correlated with neutralizing antibody titers in acute and convalescent phases but, importantly, they did not associate with LTD. Acute RSV pre-F exclusive and post-F IgG titers negatively correlated with patient age (P = 0.0007 and P < 0.0001), while a positive correlation was observed between the fold changes in RSV F-specific antibody titers between convalescent and acute phase and patient age (P = 0.0014 and P < 0.0001). Infants ≤2 months exhibited significantly lower fold-changes in RSV F-specific and neutralizing antibody titers between convalescence and acute phase than older infants. Additionally, acute RSV antibody titers showed no correlation with nasal RSV load and, furthermore, nasal viral load was not associated with the development of LTD.

CONCLUSIONS

This study highlights that protection against life-threatening RSV disease is not necessarily antibody-dependent. Further characterization of the immune response against RSV and its role in protection against severe disease is important for the development of the safest possible preventive strategies.

Longitudinal humoral analysis in RSV-infected infants identifies pre-existing RSV strain-specific G and evolving cross-reactive F antibodies

Respiratory syncytial virus (RSV) is among the most common causes of lower respiratory tract infection (LRTI) and hospitalization in infants. However, the mechanisms of immune control in infants remain incompletely understood. Antibody profiling against attachment (G) and fusion (F) proteins in children less than 2 years of age, with mild (outpatients) or severe (inpatients) RSV disease, indicated substantial age-dependent differences in RSV-specific immunity. Maternal antibodies were detectable for the first 3 months of life, followed by a long window of immune vulnerability between 3 and 6 months and a rapid evolution of FcγR-recruiting immunity after 6 months of age. Acutely ill hospitalized children exhibited lower G-specific antibodies compared with healthy controls. With disease resolution, RSV-infected infants generated broad functional RSV strain-specific G-responses and evolved cross-reactive F-responses, with minimal maternal imprinting. These data suggest an age-independent RSV G-specific functional humoral correlate of protection, and the evolution of RSV F-specific functional immunity with disease resolution.

Difference in respiratory syncytial virus-specific Fc-mediated antibody effector functions between children and adults

Respiratory syncytial virus (RSV) infections are a major cause of bronchiolitis and pneumonia in infants and older adults, for which there is no known correlate of protection. Increasing evidence suggests that Fc-mediated antibody effector functions have an important role, but little is known about the development, heterogeneity, and durability of these functional responses. In light of future vaccine strategies, a clear view of the immunological background and differences between various target populations is of crucial importance. In this study, we have assessed both quantitative and qualitative aspects of RSV-specific serum antibodies, including IgG/IgA levels, IgG subclasses, antibody-dependent complement deposition, cellular phagocytosis, and NK cell activation (ADNKA). Samples were collected cross-sectionally in different age groups (11-, 24-, and 46-month-old children, adults, and older adults; n = 31-35 per group) and longitudinally following natural RSV infection in (older) adults (2-36 months post-infection; n = 10). We found that serum of 24-month-old children induces significantly lower ADNKA than the serum of adults (P < 0.01), which is not explained by antibody levels. Furthermore, in (older) adults we observed boosting of antibody levels and functionality at 2-3 months after RSV infection, except for ADNKA. The strongest decrease was subsequently observed within the first 9 months, after which levels remained relatively stable up to three years post-infection. Together, these data provide a comprehensive overview of the functional landscape of RSV-specific serum antibodies in the human population, highlighting that while antibodies reach adult levels already at a young age, ADNKA requires more time to fully develop.

A Pseudovirus-Based Entry Assay to Evaluate Neutralizing Activity against Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) infection can cause life-threatening pneumonia and bronchiolitis, posing a significant threat to human health worldwide, especially to children and the elderly. Currently, there is no specific treatment for RSV infection. The most effective measures for preventing RSV infection are vaccines and prophylactic medications. However, not all population groups are eligible for the approved vaccines or antibody-based preventive medications. Therefore, there is an urgent need to develop novel vaccines and prophylactic drugs available for people of all ages. High-throughput assays that evaluate the efficacy of viral entry inhibitors or vaccine-induced neutralizing antibodies in blocking RSV entry are crucial for evaluating vaccine and prophylactic drug candidates. We developed an efficient entry assay using a lentiviral pseudovirus carrying the fusion (F) protein of type A or B RSV. In addition, the essential parameters were systematically optimized, including the number of transfected plasmids, storage conditions of the pseudovirus, cell types, cell numbers, virus inoculum, and time point of detection. Furthermore, the convalescent sera exhibited comparable inhibitory activity in this assay as in the authentic RSV virus neutralization assay. We established a robust pseudovirus-based entry assay for RSV, which holds excellent promise for studying entry mechanisms, evaluating viral entry inhibitors, and assessing vaccine-elicited neutralizing antibodies against RSV.

Recent updates on correlates of vaccine-induced protection

Correlates of protection are key for vaccine development against any pathogen. In this paper we summarize recent information about correlates for vaccines against dengue, Ebola, influenza, pneumococcal, respiratory syncytial virus, rotavirus, shigella, tuberculosis and Zika virus.

Retrospective comparison of respiratory syncytial virus and metapneumovirus clinical presentation in hospitalized children

Respiratory syncytial virus (RSV) and Human metapneumovirus (hMPV), members of Pneumoviridae family are common causes of acute respiratory tract infections (ARTI) among children. Study material includes routine nasopharyngeal samples obtained during 8-year period for hMPV and one single season for RSV in children hospitalized for ARTI between 0 and 15 years at the Center Hospitalier Universitaire (CHU) Saint Pierre in Brussels. Positive samples for RSV or hMPV identified by viral culture, lateral flow chromatography test for RSV or direct fluorescent assay for hMPV were selected retrospectively. Characteristics of children hospitalized for RSV or hMPV infections were compared. Children hospitalized for RSV infection were significantly younger and requiring more respiratory support, longer hospital stay and transfers in Pediatric intensive Care Units than those hospitalized for hMPV infection. Pneumonia diagnostic and antibiotics therapies were more significantly associated with hMPV infections. In conclusion, despite their genetic similarities, RSV, and hMPV present epidemiological and clinical differences in pediatric infections. Our results should be confirmed prospectively.

A prefusion-stabilized RSV F subunit vaccine elicits B cell responses with greater breadth and potency than a postfusion F vaccine

There is currently no licensed vaccine for respiratory syncytial virus (RSV). Here, we assess the effect of RSV fusion protein (F) conformation on B cell responses in a post hoc comparison of samples from the DS-Cav1 [prefusion (pre-F)] and MEDI7510 [postfusion (post-F)] vaccine clinical trials. We compared the magnitude and quality of the serological and B cell responses across time points and vaccines. We measured RSV A and B neutralization, F-binding immunoglobulin G titers, and competition assays at week 0 (before vaccination) and week 4 (after vaccination) to evaluate antibody specificity and potency. To compare B cell specificity and activation, we used pre-F and post-F probes in tandem with a 17-color immunophenotyping flow cytometry panel at week 0 (before vaccination) and week 1 (after vaccination). Our data demonstrate that both DS-Cav1 and MEDI7510 vaccination robustly elicit F-specific antibodies and B cells, but DS-Cav1 elicited antibodies that more potently neutralized both RSV A and B. The superior potency was mediated by antibodies that bind antigenic sites on the apex of pre-F that are not present on post-F. In the memory (CD27+) B cell compartment, vaccination with DS-Cav1 or MEDI7510 elicited B cells with different epitope specificities. B cells preferentially binding the pre-F probe were activated in DS-Cav1-vaccinated participants but not in MEDI7510-vaccinated participants. Our findings emphasize the importance of using pre-F as an immunogen in humans because of its deterministic role in eliciting highly potent neutralizing antibodies and memory B cells.

RSV disease in infants and young children: Can we see a brighter future?

Respiratory syncytial virus (RSV) is a highly contagious seasonal virus and the leading cause of Lower Respiratory Tract Infections (LRTI), including pneumonia and bronchiolitis in children. RSV-related LRTI cause approximately 3 million hospitalizations and 120,000 deaths annually among children <5 years of age. The majority of the burden of RSV occurs in previously healthy infants. Only a monoclonal antibody (mAb) has been approved against RSV infections in a restricted group, leaving an urgent unmet need for a large number of children potentially benefiting from preventive measures. Approaches under development include maternal vaccines to protect newborns, extended half-life monoclonal antibodies to provide rapid long-lasting protection, and pediatric vaccines. RSV has been identified as a major global priority but a solution to tackle this unmet need for all children has yet to be implemented. New technologies represent the avenue for effectively addressing the leading-cause of hospitalization in children <1 years old.

Immunopathology of RSV: An Updated Review

RSV is a leading cause of respiratory tract disease in infants and the elderly. RSV has limited therapeutic interventions and no FDA-approved vaccine. Gaps in our understanding of virus-host interactions and immunity contribute to the lack of biological countermeasures. This review updates the current understanding of RSV immunity and immunopathology with a focus on interferon responses, animal modeling, and correlates of protection.