Preventing respiratory syncytial virus (RSV) disease in children

Epidemiology of pediatric dengue virus infection, Scenario from a tertiary level hospital in Bangladesh

BACKGROUND

Dengue fever is the most rapidly spreading mosquito-borne disease and has grown to be a major public health issue, especially in tropical nations like Bangladesh. Globally, children, adolescents, and young adults bear the largest burden of Dengue; the infection rate is highest among infants. However, the epidemiology of pediatric dengue virus infection has been poorly explored in Bangladesh.

MATERIALS AND METHODS

This study was carried out at the Bangladesh Shishu Hospital & Institute from July to October 2023. Among 1102 admitted patients, 722 who were positive for dengue rapid test were enrolled.

RESULTS

The highest number of positive patients were 1-5 years old (38 %) followed by 5-10 years (32 %). Vomiting (49 %) was most common after fever (100 %). 71 % of patients showed warning signs, with 17 deaths. All patients received antibiotics, and the number of different antibiotics increased with hospital stay. Real-time RT-PCR was conducted on purposively selected 104 rapid test positives and 50 negatives for serotyping. DENV-2 was the most predominant serotype (80 %), followed by DENV-3 (20 %).

CONCLUSION

This study underscored the need for targeted public health interventions, especially for children with warning signs, to address the high burden of pediatric dengue infection in Bangladesh.

Photoinduced Cleavage of Respiratory Syncytial Virus by Chiral Vanadium Trioxide Nanoparticles

Respiratory syncytial virus (RSV) poses a significant threat to the health of infants, children, and the elderly, and as of now there is a lack of effective therapeutic drugs. To tackle this challenge, chiral vanadium trioxide nanoparticles (V2O3 NPs) with a particle size of 2.56 ± 0.34 nm are successfully synthesized, exhibiting a g-factor value of 0.048 at 874 nm in terms of circular dichroism. Under 808 nm light irradiation, these chiral V2O3 NPs demonstrated selective cleavage of the RSV pre-fusion protein (RSV protein), effectively blocking its conformational rearrangement and preventing RSV infection both in vitro and in vivo. Experimental analysis revealed that the chiral V2O3 NPs specifically bind to the functional domain spanning from aspartate200 (D200) to asparagine208 (N208) in the primary sequence of the RSV protein. Notably, L-V2O3 NPs exhibited a higher affinity, which is 4.06 times that of D-V2O3 NPs and 13.55 times that of DL-V2O3 NPs. The precise cutting site is located between amino acid residues leucine204 (L204) and proline205 (P205), attributed to the reactive oxygen species (ROS) generated by photoinduced nanoparticles. In addition, L-V2O3 NPs inhibited RSV infection by 99.6% in nasal epithelial cells and 99.2% in Vero cells. In the RSV-infected mouse model, intranasal administration of L-V₂O₃ NPs effectively controlled the viral load in the lungs of mice, reducing it by 92.43%. The hematoxylin and eosin staining of mouse organs and serum biochemical indicators are similar to those of the wild-type group, indicating the biosafety of L-V₂O₃ NPs. The findings suggest that chiral nanoparticles hold great potential in controlling RSV and provide new directions and ideas for drug development against viruses.

Multi-scenario surveillance of respiratory viruses in aerosols with sub-single-copy spatial resolution

Highly sensitive airborne virus monitoring is critical for preventing and containing epidemics. However, the detection of airborne viruses at ultra-low concentrations remains challenging due to the lack of ultra-sensitive methods and easy-to-deployment equipment. Here, we present an integrated microfluidic cartridge that can accurately detect SARS-COV-2, Influenza A, B, and respiratory syncytial virus with a sensitivity of 10 copies/mL. When integrated with a high-flow aerosol sampler, our microdevice can achieve a sub-single-copy spatial resolution of 0.83 copies/m3 for airborne virus surveillance with an air flow rate of 400 L/min and a sampling time of 30 minutes. We then designed a series of virus-in-aerosols monitoring systems (RIAMs), including versions of a multi-site sampling RIAMs (M-RIAMs), a stationary real-time RIAMs (S-RIAMs), and a roaming real-time RIAMs (R-RIAMs) for different application scenarios. Using M-RIAMs, we performed a comprehensive evaluation of 210 environmental samples from COVID-19 patient wards, including 30 aerosol samples. The highest positive detection rate of aerosol samples (60%) proved the aerosol-based SARS-CoV-2 monitoring represents an effective method for spatial risk assessment. The detection of 78 aerosol samples in real-world settings via S-RIAMs confirmed its reliability for ultra-sensitive and continuous airborne virus monitoring. Therefore, RIAMs shows the potential as an effective solution for mitigating the risk of airborne virus transmission.

Respiratory syncytial virus vaccination and immunoprophylaxis: realising the potential for protection of young children

The search for safe and efficacious products to prevent severe respiratory syncytial virus (RSV) disease in young infants has lasted more than 60 years. In high-income and middle-income countries, two new products have been authorised: an RSV monoclonal antibody for administration to infants (nirsevimab) and an RSV prefusion F maternal vaccine (RSVpreF [Pfizer, Puurs, Belgium]) for administration to pregnant people. These products are not yet available in low-income and lower-middle-income countries, where most RSV deaths occur. Other papers in this Series describe the acute burden of RSV disease in young children, the effects of RSV infection in early childhood on long-term lung health, and the burden of RSV disease and disease prevention products in older adults. In this Series paper, we briefly review the efficacy, effectiveness, and safety of nirsevimab and RSVpreF maternal vaccine for protection of infants. We then explore potential regulatory, policy, and implementation pathways and provide case studies of intervention uptake in Spain and Argentina, and considerations for use in Kenya. We also explore the health economic evidence to inform product introduction decisions. With sufficient political will and affordable pricing, RSV disease prevention in infants can become a global reality.

Evaluation of the Live-Attenuated Intranasal Respiratory Syncytial Virus (RSV) Vaccine RSV/6120/ΔNS2/1030s in RSV-Seronegative Young Children

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of pediatric lower respiratory illness (LRI) and a vaccine for immunization of children is needed. RSV/6120/ΔNS2/1030s is a cDNA-derived live-vaccine candidate attenuated by deletion of the interferon antagonist NS2 gene and the genetically stabilized 1030s missense polymerase mutation in the polymerase, conferring temperature sensitivity.

METHODS

A single intranasal dose of RSV/6120/ΔNS2/1030s was evaluated in a double-blind, placebo-controlled trial (vaccine to placebo ratio, 2:1) at 105.7 plaque-forming units (PFU) in 15 RSV-seropositive 12- to 59-month-old children, and at 105 PFU in 30 RSV-seronegative 6- to 24-month-old children.

RESULTS

RSV/6120/ΔNS2/1030s infected 100% of RSV-seronegative vaccinees and was immunogenic (geometric mean RSV plaque-reduction neutralizing antibody titer [RSV-PRNT], 1:91) and genetically stable. Mild rhinorrhea was detected more frequently in vaccinees (18/20 vaccinees vs 4/10 placebo recipients, P = .007), and LRI occurred in 1 vaccinee during a period when only vaccine virus was detected. Following the RSV season, 5 of 16 vaccinees had ≥4-fold rises in RSV-PRNT with significantly higher titers than 4 of 10 placebo recipients with rises (1:1992 vs 1:274, P = .02). Thus, RSV/6120/ΔNS2/1030s primed for substantial anamnestic neutralizing antibody responses following naturally acquired RSV infection.

CONCLUSIONS

RSV/6120/ΔNS2/1030s is immunogenic and genetically stable in RSV-seronegative children, but the frequency of rhinorrhea in vaccinees exceeded that in placebo recipients.

CLINICAL TRIALS REGISTRATION

NCT03387137.

Burden of Respiratory Syncytial Virus in the European Union: estimation of RSV-associated hospitalizations in children under 5 years

BACKGROUND

No overall estimate of respiratory syncytial virus (RSV)-associated hospitalizations in children aged under 5 years has been published for the European Union (EU). We aimed to estimate the RSV hospitalization burden in children aged under 5 years in EU countries and Norway, by age group.

METHODS

We collated national RSV-associated hospitalization estimates calculated using linear regression models via the RESCEU project for Denmark, England, Finland, Norway, the Netherlands, and Scotland, 2006-2018. Additional estimates were obtained from a systematic review. Using multiple imputation and nearest neighbor matching methods, we estimated overall RSV-associated hospitalizations and rates in the EU.

RESULTS

Additional estimates for 2 countries (France and Spain) were found in the literature. In the EU, an average of 245 244 (95% confidence interval [CI], 224 688-265 799) yearly hospital admissions with a respiratory infection per year were associated with RSV in children aged under 5 years, with most cases occurring among children aged under 1 year (75%). Infants aged under 2 months represented the most affected group (71.6 per 1000 children; 95% CI, 66.6-76.6).

CONCLUSIONS

Our findings will help support decisions regarding prevention efforts and represent an important benchmark to understand changes in the RSV burden following the introduction of RSV immunization programs in Europe.

Value profile for respiratory syncytial virus vaccines and monoclonal antibodies

Respiratory syncytial virus (RSV) is the predominant cause of acute lower respiratory infection (ALRI) in young children worldwide, yet no licensed RSV vaccine exists to help prevent the millions of illnesses and hospitalizations and tens of thousands of young lives taken each year. Monoclonal antibody (mAb) prophylaxis exists for prevention of RSV in a small subset of very high-risk infants and young children, but the only currently licensed product is impractical, requiring multiple doses and expensive for the low-income settings where the RSV disease burden is greatest. A robust candidate pipeline exists to one day prevent RSV disease in infant and pediatric populations, and it focuses on two promising passive immunization approaches appropriate for low-income contexts: maternal RSV vaccines and long-acting infant mAbs. Licensure of one or more candidates is feasible over the next one to three years and, depending on final product characteristics, current economic models suggest both approaches are likely to be cost-effective. Strong coordination between maternal and child health programs and the Expanded Program on Immunization will be needed for effective, efficient, and equitable delivery of either intervention. This 'Vaccine Value Profile' (VVP) for RSV is intended to provide a high-level, holistic assessment of the information and data that are currently available to inform the potential public health, economic and societal value of pipeline vaccines and vaccine-like products. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, public private partnerships and multi-lateral organizations, and in collaboration with stakeholders from the WHO headquarters. All contributors have extensive expertise on various elements of the RSV VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.

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.

A scientometrics study of the nanomedicines assisted in respiratory diseases

Nanomedicine has been extensively studied for its versatility and broad-spectrum applications of theranostics in the research of respiratory disease. However, to the best of our knowledge, a scientometrics study based on the scientific knowledge assay of the overall situation on nanomedicine applied in the research of respiratory disease has not been reported so far, which would be of major importance to relevant researchers. To explore and exhibit the research status and developing trend of nanomedicines deployed in basic or clinical research in respiratory disease, the research ecosystem and exciting subareas were profiled based on the massive data mining and visualization from the relevant works reported from 2006 to 2021. Data were collected from the Web of Science database. Data statistics software and bibliometric analysis software were employed to visualize the research trend and the relationship between respiratory diseases and nanomedicines in each representative direction. The cluster analysis and burst detections indicated that the improvement of drug delivery and vaccine developments are the up-to-date key directions in nanomedicines for respiratory disease research and treatments. Furthermore, we emphatically studied four branch areas in this field including COVID-19, nanotube, respiratory syncytial virus, and mRNA vaccine those are selected for in-depth mining and bibliometric coupling analysis. Research trends signify the future focuses will center on preventing respiratory diseases with mRNA vaccines using nanoparticle-based approaches. We anticipate our study will enable researchers to have the panorama and deep insights in this area, thus inspiriting further exploitations especially the nanobiomaterial-based systems for theranostic applications in respiratory disease treatment.

Predicted effectiveness of vaccines and extended half-life monoclonal antibodies against RSV hospitalizations in children

Several vaccines and extended half-life monoclonal antibodies (mAbs) against respiratory syncytial virus (RSV) have shown promise in clinical trials. We used age-structured transmission models to predict the possible impact of various RSV prevention strategies including maternal immunization, live-attenuated vaccines, and long-lasting mAbs. Our results suggest that maternal immunization and long-lasting mAbs are likely to be highly effective in preventing RSV hospitalizations in infants under 6 months of age, averting more than half of RSV hospitalizations in neonates. Live-attenuated vaccines could reduce RSV hospitalizations in vaccinated age groups and are also predicted to have a modest effect in unvaccinated age groups because of disruptions to transmission. Compared to year-round vaccination, a seasonal vaccination program at the country level provides at most a minor advantage regarding efficiency. Our findings highlight the substantial public health impact that upcoming RSV prevention strategies may provide.

Level of maternal antibodies against respiratory syncytial virus (RSV) nucleoprotein at birth and risk of RSV very severe lower respiratory tract infection

BACKGROUND

The nucleoprotein (N protein) of respiratory syncytial virus (RSV) is a candidate antigen for new RSV vaccine development. The aim of the present study was to investigate the association between maternal antibody titers against the RSV N protein at birth and the newborns' risk of developing very severe lower respiratory tract infection (VS-LRTI).

METHODS

In this single-center prospective cohort study, 578 infants born during the RSV epidemic season in France were included. Among these, 36 were hospitalized for RSV VS-LRTI. A generalized linear model was used to test the occurrence of a VS-LRTI in function of sex, mode of delivery, parity of the mother, type of pregnancy, date of birth in relation to the peak of the epidemic, and antibody titer against N protein.

RESULTS

All cord blood samples had detectable antibodies against N protein. The mean titers were significantly lower in newborns with risk factors for RSV severe LRTI (preterm infants, birth before the peak epidemic, multiparous mother). There was no association between antibody titer against the N protein and a protection against VS-LRTI.

CONCLUSIONS

Further studies are needed to support the hypothesis that transfer of maternal antibodies against the RSV N protein can provide a significant immune protection early in infancy and that N protein candidate vaccine may be a suitable target for maternal vaccine.

Stability Study, Quantification Method and Pharmacokinetics Investigation of a Coumarin-Monoterpene Conjugate Possessing Antiviral Properties against Respiratory Syncytial Virus

The stability of a new coumarin derivative, agent K-142, bearing α-pinene residue and possessing antiviral activity against respiratory syncytial virus (RSV) was studied in whole mice blood in vitro, and a method for its quantification in this matrix was developed and validated. The sample preparation method was precipitation of whole blood with a mixture of 0.2 M ZnSO4 with MeOH (2:8 v/v) containing 2-adamantylamine hydrochloride as an internal standard (IS). Analysis was carried out by HPLC-MS/MS using reversed phase chromatography and a triple quadrupole mass spectrometer 6500 QTRAP (SCIEX) in multiple reaction monitoring (MRM) mode. The transitions 351.2 → 217.1 Da and 152.2 → 93.1/107.2 Da were monitored for K-142 and the IS, respectively. The method was validated in terms of selectivity, calibration curve, LLOQ, accuracy and precision, stability, recovery and carry over. The developed method was used for a pharmacokinetics study of the compound after its oral administration to mice at a dose of 20 mg/kg.

Systematic Literature Review of Respiratory Syncytial Virus Laboratory Testing Practices and Incidence in United States Infants and Children <5 Years of Age

Background

Respiratory syncytial virus (RSV) can cause serious illness in those aged <5 years in the United States, but uncertainty remains around which populations receive RSV testing. We conducted a systematic literature review of RSV testing patterns in studies published from 2000 to 2021.

Methods

Studies of RSV, medically attended RSV lower respiratory tract infections (LRTIs), and bronchiolitis were identified using standard methodology. Outcomes were clinical decisions to test for RSV, testing frequency, and testing incidence proportions in inpatient (IP), emergency department (ED), outpatient (OP), and urgent care settings.

Results

Eighty good-/fair-quality studies, which reported data from the period 1988–2020, were identified. Twenty-seven described the clinical decision to test, which varied across and within settings. Two studies reported RSV testing frequency for multiple settings, with higher testing proportions in IP (n = 2, range: 83%–85%, 1996–2009) compared with ED (n = 1, 25%, 2006–2009) and OP (n = 2, 15%–25%, 1996–2009). Higher RSV testing incidence proportions were observed among LRTI infant populations in the ED (n = 1, 74%, 2007–2008) and OP (n = 2, 54%–69%, 1995–2008). Incidence proportions in LRTI populations were not consistently higher in the IP setting (n = 13). Across studies and time, there was heterogeneity in RSV testing patterns, which may reflect varying detection methods, populations, locations, time periods, and healthcare settings.

Conclusions

Not all infants and children with LRTI are tested for RSV, highlighting underestimation of RSV burden across all settings.

Challenges in Maximizing Impacts of Preventive Strategies against Respiratory Syncytial Virus (RSV) Disease in Young Children

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract illness in infants and young children. It causes substantial morbidity and mortality in young children and older adults. As few therapeutic and prophylaxis options against RSV illness are currently available, there is a great need for effective RSV vaccines and immune-prophylaxis. Encouragingly, multiple vaccines and immuno-prophylaxis aiming to protect pediatric populations have shown promising progress in clinical trials. The three major preventive strategies include RSV F-protein-based vaccines for pregnant women, extended half-life monoclonal antibodies for neonates, and live-attenuated vaccines for infants. Each preventive strategy has its own merits and challenges yet to be overcome. Challenges also exist in maximizing vaccine impacts in the post-implementation era. This perspectives piece focuses on RSV preventive strategies in young children and highlights the remaining questions in current development of RSV immunization products and design of immunization programs.

WHO preferred product characteristics for monoclonal antibodies for passive immunization against respiratory syncytial virus (RSV) disease in infants - Key considerations for global use

World Health Organization (WHO) preferred product characteristics describe preferences for product attributes that would help optimize value and use to address global public health needs, with a particular focus on low- and middle-income countries. Having previously published preferred product characteristics for both maternal and paediatric respiratory syncytial virus (RSV) vaccines, WHO recently published preferred product characteristics for monoclonal antibodies to prevent severe RSV disease in infants. This article summarizes the key attributes from the preferred product characteristics and discusses key considerations for future access and use of preventive RSV monoclonal antibodies.

Binding and neutralizing antibody responses to SARS-CoV-2 in young children exceed those in adults

Background

SARS-CoV-2 infections are frequently milder in children than adults, suggesting that immune responses may vary with age. However, information is limited regarding SARS-CoV-2 immune responses in young children.

Methods

We compared receptor binding domain–binding antibody (RBDAb) titers and SARS-CoV-2–neutralizing antibody titers, measured by pseudovirus-neutralizing antibody assay in serum specimens obtained from children aged 0–4 years and 5–17 years and in adults aged 18–62 years at the time of enrollment in a prospective longitudinal household study of SARS-CoV-2 infection.

Results

Among 56 seropositive participants at enrollment, children aged 0–4 years had more than 10-fold higher RBDAb titers than adults (416 vs. 31, P < 0.0001) and the highest RBDAb titers in 11 of 12 households with seropositive children and adults. Children aged 0–4 years had only 2-fold higher neutralizing antibody than adults, resulting in higher binding-to-neutralizing antibody ratios compared with adults (2.36 vs. 0.35 for ID₅₀, P = 0.0004).

Conclusion

These findings suggest that young children mount robust antibody responses to SARS-CoV-2 following community infections. Additionally, these results support using neutralizing antibody to measure the immunogenicity of COVID-19 vaccines in children aged 0–4 years.

Funding

CDC (award 75D30120C08737).

OUP accepted manuscript

Background

Respiratory syncytial virus (RSV) is the leading cause of hospitalizations in United States infants aged <1 year, but research has focused on select populations.

Methods

National (Nationwide) Inpatient Sample and National Emergency Department (ED) Sample data (2011–2019) were used to report RSV hospitalization (RSVH), bronchiolitis hospitalization (BH), and ED visit counts, percentage of total hospitalizations/visits, and rates per 1000 live births along with inpatient mortality, mechanical ventilation (MV), and total charges (2020 US dollars).

Results

Average annual RSVH and RSV ED visits were 56 927 (range, 43 845–66 155) and 131 999 (range, 89 809–177 680), respectively. RSVH rates remained constant over time (P = .5), whereas ED visit rates increased (P = .004). From 2011 through 2019, Medicaid infants had the highest average rates (RSVH: 22.3 [95% confidence interval {CI}, 21.5–23.1] per 1000; ED visits: 55.9 [95% CI, 52.4–59.4] per 1000) compared to infants with private or other/unknown insurance (RSVH: P < .0001; ED visits: P < .0001). From 2011 through 2019, for all races and ethnicities, Medicaid infants had higher average RSVH rates (up to 7 times) compared to infants with private or other/unknown insurance. RSVH mortality remained constant over time (P = .8), whereas MV use (2019: 13% of RSVH, P < .0001) and mean charge during hospitalization (2019: $21 513, P < .0001) increased. Bronchiolitis patterns were similar.

Conclusions

This study highlights the importance of ensuring access to RSV preventive measures for all infants.

OUP accepted manuscript

Background

This study describes leading causes of hospitalization, including respiratory syncytial virus (RSV), in United States infants (<1 year) from 2009 through 2019.

Methods

Within the National (Nationwide) Inpatient Sample (NIS) data, hospitalizations were determined by primary diagnosis using International Classification of Diseases, Ninth or Tenth Revision codes. RSV was defined as 079.6, 466.11, 480.1, B97.4, J12.1, J20.5, or J21.0. Bronchiolitis was defined as 466.19, J21.8, or J21.9. Leading causes overall and by sociodemographic variables were identified. The Kids’ Inpatient Database (KID) was used for confirmatory analyses.

Results

Acute bronchiolitis due to RSV (code 466.11 or J21.0) was the leading primary diagnosis, accounting for 9.6% (95% confidence interval [CI], 9.4%–9.9%) and 9.3% (95% CI, 9.0%–9.6%) of total infant hospitalizations from January 2009 through September 2015 and October 2015 through December 2019, respectively; it was the leading primary diagnosis in every year accounting for >10% of total infant hospitalizations from December through March, reaching >15% in January–February. From 2009 through 2011, acute bronchiolitis due to RSV was the leading primary diagnosis in every birth month. Acute bronchiolitis due to RSV was the leading cause among all races/ethnicities, except Asian/Pacific Islanders, and all insurance payer groups. KID analyses confirmed these results.

Conclusions

Acute bronchiolitis due to RSV is the leading cause of US infant hospitalizations.

Binding and Neutralizing Antibody Responses to SARS-CoV-2 in Infants and Young Children Exceed Those in Adults

SARS-CoV-2 infections are frequently milder in children than adults, suggesting that immune responses may vary with age. However, information is limited regarding SARS-CoV-2 immune responses in young children. We compared Receptor Binding Domain binding antibody (RBDAb) and SARS-CoV-2 neutralizing antibody (neutAb) in children aged 0-4 years, 5-17 years, and in adults aged 18-62 years in a SARS-CoV-2 household study. Among 55 participants seropositive at enrollment, children aged 0-4 years had >10-fold higher RBDAb titers than adults (373 vs.35, P <0.0001), and the highest RBDAb titers in 11/12 households with seropositive children and adults. Children aged 0-4 years had 2-fold higher neutAb than adults, resulting in higher binding to neutralizing (B/N)Ab ratios compared to adults (1.9 vs. 0.4 for ID 50 , P=0.0002). Findings suggest that young children mount robust antibody responses to SARS-CoV-2 following community infections. Additionally, these results support using neutAb to measure the immunogenicity of COVID-19 vaccines in children aged 0-4 years.

Monoterpene-Containing Substituted Coumarins as Inhibitors of Respiratory Syncytial Virus (RSV) Replication

Respiratory syncytial virus (RSV) is a critical cause of infant mortality. However, there are no vaccines and adequate drugs for its treatment. We showed, for the first time, that O-linked coumarin-monoterpene conjugates are effective RSV inhibitors. The most potent compounds are active against both RSV serotypes, A and B. According to the results of the time-of-addition experiment, the conjugates act at the early stages of virus cycle. Based on molecular modelling data, RSV F protein may be considered as a possible target.

Monocytes Contribute to IFN-β Production via the MyD88-Dependent Pathway and Cytotoxic T-Cell Responses against Mucosal Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is the leading cause of respiratory viral infection in infants and children. However, little is known about the contribution of monocytes to antiviral responses against RSV infection. We identified the IFN-β production of monocytes using IFN-β/YFP reporter mice. The kinetic analysis of IFN-β-producing cells in in vivo RSV-infected lung cells indicated that monocytes are recruited to the inflamed lung during the early phase of infection. These cells produced IFN-β via the myeloid differentiation factor 88-mediated pathway, rather than the TLR7- or mitochondrial antiviral signaling protein-mediated pathway. In addition, monocyte-ablated mice exhibited decreased numbers of IFN-γ-producing and RSV Ag-specific CD8⁺ T cells. Collectively, these data indicate that monocytes play pivotal roles in cytotoxic T-cell responses and act as type I IFN producers during RSV infection.