Presentación de trabajos libres (Libro de resúmenes on-line)

Introducción:
La vacunación materna con dTpa, incorporada en Argentina en 2012, ha demostrado impacto en la reducción de la morbimortalidad por coqueluche en lactantes <6 meses. Los objetivos fueron describir los cambios en las características epidemiológicas, clínicas y desenlaces de los casos confirmados antes y después de la implementación y analizar la influencia de la pandemia de COVID-19 en la circulación.

Material y métodos:
Estudio observacional antes-después basado en vigilancia epidemiológica activa en un hospital pediátrico de referencia (2004–2025). Se incluyeron casos confirmados por laboratorio (PCR y/o cultivo positivo para Bordetella pertussis) y se compararon dos períodos: pre-intervención (PreV: 2004-2011) y post-intervención (PostV: 2013-2025), excluyendo 2012 (año de transición). Se compararon las variables demográficas, clínicas y de evolución en ambos períodos. Se calculó la reducción relativa de tasas de hospitalización (por 10.000 egresos) y letalidad (%), con sus intervalos de confianza (IC) del 95% y p-valor. El análisis estadístico se realizó con R (R Foundation for Statistical Computing, Austria).

Resultados:
Se identificaron 384 casos confirmados de coqueluche (232 Pre-V y 152 Post-V). La mediana de edad fue mayor en el Post-V (3 vs 12 meses; p<0,001). La distribución etaria mostró un descenso de proporción de lactantes <6 meses (81,0% vs 29,6%; p<0,001) y un aumento en el grupo de 6 meses-4 años (17,2% vs 59,9%; p<0,001). Los casos hospitalizados representaron el 87,1% en el PreV y 55,9% en el PostV (p<0,001). La tasa de hospitalización se redujo 67,5% (IC95%: 58,9–74,6; p<0,001). La letalidad descendió del 6,0% al 1,3%, con reducción relativa del 78,2% (IC95%: 4,1–95,0; p=0,044). La distribución por sexo, comorbilidades, asistencia respiratoria mecánica y días de internación no mostraron diferencias significativas entre los periodos. Entre los años 2020 y 2023 se registró un solo caso de coqueluche. En 2025 hasta la SE 30 se registraron 38 casos. En 2024 se registró el último fallecido.

Conclusiones:
Tras la vacunación materna con dTpa, se evidenció un cambio en el perfil epidemiológico de coqueluche, con menor hospitalización, letalidad, y desplazamiento de la carga de enfermedad hacia grupos mayores. No obstante, la reemergencia observada en el período post pandemia subraya la necesidad de lograr altas coberturas para el esquema primario y de sostener la estrategia de vacunación materna.

Background: Studies have shown that detection of specific potentially pathogenic bacteria (PPB) in the nasopharynx (NP) of children with RSV infection is associated with a distinct systemic immune profiles and worse clinical outcomes. Whether those PPB alter mucosal innate immunity responses and vary according to age is not fully known

Objective: To define whether specific NP bacteria induce a distinct mucosal cytokine response and worse disease severity in infants and young children with RSV infection

Methods: Prospective observational study of otherwise healthy children <2 years of age with mild (outpatients-OP-) or severe (inpatients- IP-) RSV infection and age matched controls (HC) from 2015-19. Four PPB were quantified via qRT-PCR in NP swabs: S. pneumoniae (Sp), S. aureus (Sa), M. catarrhalis (Mc), and H. influenzae (Hi). Mucosal cytokine concentrations were measured using a 13-plex panel that included antiviral (type I, II, and III interferons -IFN-), pro-, and anti-inflammatory cytokines. Disease severity was analyzed according to NP PPB detection. Study was approved by the Hospital Institutional Review Board

Results: We enrolled 214 infants with RSV infection [78 OP (36%), 136 IP (64%)], and 33 HC. NP PPB were identified in 89% of RSV+ children vs 78% of HC, with different patterns of PPB according to infection status. Detection of Hi (5 vs 0%) and >1PPB (61 vs 36%; p<0.01) was greater in RSV+ infants vs HC, while Sa was more frequent in HC (21 vs 6%; p<0.001). These differences were more evident in older children (>6 mo). Overall, children with RSV infection and any PPB, had higher mucosal IFNa, IL-1β, IL-8, and TNFα than those with no PPB. Within RSV+ children, NP detection of Hi vs other PPB was associated with higher concentrations of IL-1β, TNFa, and IL-8, while Sp detection showed higher concentrations of IFNa and IFNl2/l3. These differences were particularly evident in infants >6 mo. Lastly, NP detection of Hi was associated with significantly higher rates of fever and greater leukocytosis, while detection of both Hi and/or Sp was associated with longer length of hospitalization

Conclusions: Mucosal innate immune cytokines in infants with RSV infection differed according to the type of NP PPB and were influenced by age. Specifically, NP detection of Sp was associated with higher concentration of mucosal IFNs, while Hi showed a more proinflammatory profile, driven by age. Detection of Sp and Hi was also associated with worse clinical outcomes

Introduction: Real-life effectiveness of nirsevimab has been reported recently however, detailed analysis of VRS prophylaxis strategies in terms of public health impact and the financial result on government budgets, is still scarce. Recent universal strategy data provides a large and unique data set which enables such analyses.

Objectives: To estimate the overall public health and financial impact of a universal immunization strategy with nirsevimab, and to separate the effects coming from the immunization of newborns vs the catch-up cohort.

Materials and methods: We use historical nationwide inpatient and outpatient care data to construct 2024 counterfactuals scenarios using advanced synthetic controls methods. The impact of the 2024 strategy is estimated by reductions in four outcomes: RSV-associated lower respiratory tract infections (LRTI) medically attended outpatient visits (MAs), pediatric ward bed-days, pediatric ICU bed-days and maternal medical leaves. We conduct estimations for the eligible cohort, then divided into the seasonal cohort and the catch-up cohort

Data: 1,712,991 hospital admissions to both public and private institutions between Jan 2019 and Nov 2024, including data in demographics, ICD-10 codes, admission and discharge dates, and basic/ICU bed usage. 76,214,819 emergency visits including daily records of emergency visits not requiring hospital admission, aggregated by ICD-10 category and age group .The Chilean universal strategy included 145,087 infants immunized between April 1st and September 30th 2024, of whom 72,246 (49·79%) were born between October 1st 2023 and March 31st 2024 (the catch-up group), and 72,841 (50·21%) born between April 1st and September 30th 2024 (the seasonal newborn cohort).

Results: The synthetic control method delivered robust statistical results showing, for the eligible population, the reduction in outcomes and the cost savings shown in Table 1 and Figure 1. Considering the savings on Palivizumab and only the eligible population, the strategy –overall– saved 65.2 million USD to the government of which 49.03% corresponds to newborns, and 50.97% to the catch-up. Given the 45.3 million usd cost of the strategy, the net benefit amounts to 19,9 million USD.

Conclusions: The use of Nirsevimab in a national universal immunization program had a significant health impact and financial benefit.

Introduction: In Lower- and Middle-Income Countries, respiratory tract infections (RTI) are a leading cause of child morbidity/mortality, yet their epidemiology remains poorly defined. We established a multi-site prospective birth cohort to investigate RTI and factors associated with progression to lower RTI (LRTI); this abstract summarizes initial findings.

Methods: This ongoing cohort study, enrolled and followed pregnant women and newborns from May 2024 to Feb 2025. Infants underwent routine study visits every 6 months and twice-weekly RTI (cough or coryza) and LRTI (+tachypnea/difficulty breathing) active surveillance via electronic app. Nasal swabs (NS) collected from symptomatic infants within 4 days of symptom onset, and asymptomatic controls, were analyzed via the TrueMark™ Respiratory Panel 2.0 (OpenArray™), targeting 31 pathogens.

Results: Among 436 infants (59 (13.5%) born to enrolled women), RTI occurred in 264 (61%), with 42 (16%) progressing to LRTI. Cumulative incidence of RTI and LRTI by 250 days of life was 65% and 12%, respectively. LRTI was associated with higher number of household members, fewer prenatal visits, lower maternal vaccination and family history of allergy. Among LRTI cases, 14% required ICU admission, and 38% received antibiotics.

NS were analyzed from 11 LRTI, 53 RTI episodes and 19 controls followed between May and Nov 2024. Bacteria were identified in NS from 82% of LRTI episodes and 100% of controls. Common viruses were rhinovirus and cytomegalovirus in symptomatic and control infants. RSV was detected at low frequencies, exclusively in symptomatic infants (18% of LRTI, 2% RTI, 0% controls).

Conclusion: There was a high incidence of RTIs that often progressed to LRTIs; this progression was influenced by prenatal care interventions. Both viruses and bacteria, were identified in NS in cases and controls. The role of NS bacteria in LRTI pathogenesis—especially during co-infections with respiratory viruses—remains a research gap. This study will assess comprehensive clinical and molecular data, including cytokines, antibody profiling, transcriptomics, and immune cell phenotype analyses to enhance understanding of disease activity and risk of LRTI progression.

Introduction

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections (LRTI) and infant mortality. In March 2024, Argentina launched maternal immunization with the RSVpreF vaccine, while Chile introduced Nirsevimab for infants under 6 months during RSV season. Since both approaches are effective, identifying infants not covered by maternal immunization could clarify the benefits of combining both strategies.

Objectives

To measure the impact and effectiveness (VE) of RSVpreF maternal immunization in Argentina during 2024, and to identify gaps in immunization coverage among infants.

Methods

Impact of RSVpreF MI on RSV-LRTI hospitalizations was assessed through a hospital-based, multicenter, retrospective surveillance cohort study, and VE was measured using a nested test-negative case-control study. Data from hospitalized infants <18 months of age were collected from 3 major hospitals since 2018. VE analysis included LRTI-hospitalized infants who were born between March 1 and November 9, 2024, and whose mothers were eligible for prenatal RSV immunization. Additionally, vaccine coverage was measured among the participants.

Results

In 2024, among the eligible infant population hospitalized for LRTI, 36.38% received maternal RSVpreF immunization (MI). At the population level, MI implementation was associated with a 33.6% (95% CI: 29.5–37.2) reduction in RSV-associated ALRTI hospitalizations in infants under 6 months compared with expected rates from previous years. The number needed to immunize to prevent one RSV-related hospitalization was 83.87 (95% CI: 65.91–185.38). Among vaccinated infants under 6 months, the adjusted vaccine effectiveness (VE) against RSV-associated ALRTI hospitalization was 66.1% (95% CI: 30.1–83.8), while VE against pediatric intensive care unit (PICU) admission reached 87.2% (95% CI: 52.6–97.0). VE was 80.8% (95% CI: 62.8–90.5) in infants under 3 months. Among infants under 6 months hospitalized for RSV-associated ALRTI in 2024, 86.17% (243/282) were not covered by maternal vaccination; of these, 19.23% were preterm (<32 weeks’ gestation) and 39.59% were born before the start of the vaccination season.

Conclusions

RSVpreF maternal immunization demonstrated high effectiveness in preventing severe RSV-related ALRTI. Among infants not covered, 58.82% were preterm or born before March 2024. Expanding vaccine coverage or combining it with monoclonal antibodies could enhance RSV disease prevention.

INTRODUCTION: NEONATAL SEPSIS IS A LEADING CAUSE OF MORBIDITY AND MORTALITY IN PRETERM INFANTS. PROCALCITONIN IS A BIOMARKER THAT INCREASES IN RESPONSE TO BACTERIAL INFECTIONS, MAKING IT USEFUL FOR EARLY DIAGNOSIS OF SEPSIS. HOWEVER, ITS PHYSIOLOGICAL ELEVATION AFTER BIRTH COMPLICATES INTERPRETATION. THIS STUDY AIMS TO DETERMINE THE OPTIMAL TIMING FOR PROCALCITONIN MEASUREMENT IN VERY LOW BIRTH WEIGHT PRETERM INFANTS TO IMPROVE EARLY SEPSIS DETECTION.

OBJECTIVE: TO DETERMINE THE OPTIMAL POSTNATAL TIMING FOR SERUM PROCALCITONIN MEASUREMENT TO IMPROVE THE DIAGNOSTIC PERFORMANCE OF EARLY-ONSET NEONATAL SEPSIS

MATERIAL AND METHODS : THIS RETROSPECTIVE STUDY WAS CONDUCTED ON NEWBORNS IN A MEXICAN NEONATAL INTENSIVE CARE UNIT BETWEEN 2018 AND 2024. THE STUDY INCLUDED NEONATES WEIGHING LESS THAN 1500 GRAMS, GESTATIONAL AGES FROM 24.2 TO 36.3 WEEKS, WHO WERE HOSPITALIZED FOR MORE THAN 21 DAYS AND HAD NO CONGENITAL MALFORMATIONS. IN ACCORDANCE WITH THE NEONATAL INTENSIVE CARE UNIT ADMISSION PROTOCOL, BLOOD SAMPLES FOR PROCALCITONIN ANALYSIS WERE COLLECTED WITHIN THE FIRST 12 HOURS UP TO THE THIRD DAY OF LIFE, BASED ON CLINICAL CRITERIA. THE SAMPLES WERE OBTAINED THROUGH UMBILICAL CATHETERS. PROCALCITONIN LEVELS WERE DETERMINED USING THE ELFA METHOD. FOR THE PURPOSES OF THIS STUDY, ONLY THE FIRST PCT MEASUREMENT WAS CONSIDERED. DATA WERE ANALYZED USING RECEIVER OPERATING CHARACTERISTIC CURVES AND STATISTICAL ANALYSIS. THE STUDY WAS APPROVED BY THE INSTITUTIONAL ETHICS COMMITTEE.

RESULTS: PROCALCITONIN LEVELS BETWEEN 13 AND 24 HOURS OF LIFE DEMONSTRATED HIGHER SENSITIVITY AND SPECIFICITY FOR EARLY-ONSET SEPSIS DETECTION COMPARED TO EARLIER MEASUREMENTS. THIS TIME FRAME REDUCED FALSE-POSITIVE RESULTS CAUSED BY PHYSIOLOGICAL POSTNATAL ELEVATION. SENSITIVITY AND SPECIFICITY WERE CALCULATED USING THE AREA UNDER THE CURVE WITH THE C STATISTIC AND THE OPTIMAL CUTOFF POINT DETERMINED BY YOUDEN’S INDEX. PROCALCITONIN VALUES AT DIFFERENT SAMPLING TIMES SHOWED BETTER SENSITIVITY IN THE 13 TO 24-HOUR INTERVAL, WITH A SENSITIVITY OF 83.7% AND A SPECIFICITY OF 60%, YIELDING AN ROC AUC OF 0.72 (95% CI: 0.61–0.83). IN CONTRAST, THE 25 TO 48-HOUR INTERVAL SHOWED LOWER SENSITIVITY (58.8%) BUT SLIGHTLY HIGHER SPECIFICITY (64.7%).

CONCLUSION: MEASURING PROCALCITONIN BETWEEN 13 AND 24 HOURS OF LIFE ENHANCES EARLY SEPSIS DETECTION WHILE MINIMIZING UNNECESSARY ANTIBIOTIC EXPOSURE. THIS TIMING OPTIMIZES CLINICAL DECISION-MAKING AND SUPPORTS ANTIBIOTIC STEWARDSHIP.

OBJECTIVE
To model RSV disease burden and population-level impact of prevention strategies on childhood asthma incidence and economic outcomes using Colombian birth cohorts (2019-2024), demonstrating effects beyond traditional hospitalization metrics through the VIRAL Network LATAM framework.
METHODS
Population-based epidemiological modeling of 2,176,845 live births (Colombian DANE 2019-2024). Applied INSPIRE study parameters: 54% first-year RSV infection rate, 50% occurring <6 months, 20.75% progression to asthma by age 5. RSV-infected infants have 43% recurrent wheeze risk vs 3% uninfected (IRR 1.41). Modeled three scenarios: 1) No intervention, 2) Maternal RSVpreF vaccination (60%, 73.9%, 92.6% coverage; 72% efficacy), 3) Hybrid strategy: 73.9% maternal vaccination + 26.1% nirsevimab for uncovered infants (76% efficacy). Calculated prevented infections, avoided asthma cases, and economic savings.
RESULTS
Baseline burden: 146,937 annual RSV infections <6 months generate 30,489 childhood asthma cases. Additionally, RSV causes 101,680 recurrent wheeze cases in year 1, 94,040 in year 2, 68,767 in year 3, and 65,241 in year 4. Maternal vaccination alone (73.9% coverage) prevents 16,223 asthma cases (53.2% reduction), saving USD$3.07 million annually. Hybrid strategy prevents 22,289 cases (73.1% reduction), saving USD$4.22 million annually. Five-year cumulative savings reach USD$84.5 million across four cohorts. The hybrid approach prevents 107,417 RSV infections yearly, averts 111,445 medical consultations and 4,458 asthma-related hospitalizations. Total burden across four cohorts: 121,958 asthma cases by age 5 without intervention versus 32,801 with hybrid strategy.
CONCLUSIONS
VIRAL Network LATAM modeling demonstrates that maternal vaccination + nirsevimab not only prevents RSV hospitalizations but also prevents 73% of RSV-associated asthma, generating massive economic impact (USD$84.5 million/5-years) and transformative public health benefits. By modeling total RSV burden beyond hospitalization metrics, we reveal the true preventable cascade: 22,000+ chronic asthma cases prevented annually. This positions universal RSV prevention through maternal vaccination + nirsevimab as Colombia's highest-impact pediatric respiratory intervention, addressing both acute RSV hospitalizations AND long-term asthma burden with unprecedented population-level benefits.