June 19, 2025

Pediatric Antibiotic Use Associated with Respiratory Syncytial Virus and Influenza in the United States, 2008-2018
Authors conducted a retrospective study of outpatient antibiotic prescriptions dispensed to children in the Optum Clinformatics™ DataMart from 2008-2018. They used negative binomial time-series models regressing weekly antibiotic prescriptions against RSV and influenza circulation measures to estimate counterfactual rates of antibiotic prescriptions in the presence and absence of RSV and influenza circulation overall, by age group, census division, and antibiotic class. They estimated 6.3% (95% confidence interval 5.2-7.3%) and 3.4% (3.1-3.8%) of antibiotic prescriptions were associated with RSV and influenza, respectively. These estimates translate to 72.6 (59.7-85.9) RSV-associated and 40.0 (35.1-45.1) influenza-associated antibiotic prescriptions per 1000 children annually. Macrolides were the antibiotic class for which RSV and influenza accounted for the greatest share of prescribing.

Effectiveness and Impact of Nirsevimab in Chile During the First Season of a National Immunization Strategy against RSV (NIRSE-CL): A Retrospective Observational Study
Roll-out of the strategy began on April 1, 2024, and ended on Sept 30, 2024, targeting infants born between April 1, 2024, and Sept 30, 2024 (seasonal newborn cohort), and infants born between Oct 1, 2023, and March 31, 2024 (catch-up cohort) in Chile. Data for 157,709 infants with complete records were extracted from the consolidated database. The median age of infants was 6·27 months (IQR 3·20–9·17). After controlling for age, sex, geographical area, and weeks of gestational age, combined effectiveness of nirsevimab (for catch-up and seasonal cohorts) against RSV-related LRTI hospitalizations was 76·41% (95% CI 72·57–79·72), against RSV-related ICU admissions was 84·94% (79·47–88·95), against all-cause LRTI hospitalizations was 66·50% (61·97–70·50), and against all-cause hospitalizations was 47·90% (44·35–51·21). They estimated a relative reduction of 77·46% in RSV-related LRTI hospitalizations, 30·05 averted cases per 1000 infants, and a number needed to immunize to prevent one RSV-related LRTI hospitalization of 35.

Safety, Tolerability, and Immunogenicity of mRNA-1345 in Adults at Increased Risk for RSV Disease Aged 18 to 59 Years
These results come from a randomized, double-blind Phase 3 trial evaluating the safety and immunogenicity of the RSV vaccine, mRNA-1345, in adults aged 18-59 years at increased risk for RSV-associated lower respiratory tract disease (LRTD). Participants received a single 50-µg (licensed dose) or 30-µg dose. Co-primary immunogenicity objectives were to demonstrate noninferiority of Day 29 RSV-A and RSV-B neutralizingantibody (nAb) geometric mean titers (GMTs) for the 50-μg dose compared to those observed in adults aged ≥60 years from the Phase 3 pivotal efficacy trial. In total, 999 participants received mRNA-1345 (50-µg, n=502; 30-µg, n=497). Most solicited adverse reactions (ARs) were mild to moderate with a median duration of 2 days. Injection-site pain, fatigue, headache, and myalgia were the most common ARs. Day 29 neutralizing antibody (nAb) geometric mean titers (GMTs) in the 50-µg group met noninferiority criteria. Immune responses were consistent across subgroups and remained above baseline through Day 181. The authors conclude: In adults aged 18-59 years at increased risk for RSV-LRTD, a 50-µg dose of mRNA-1345 was well-tolerated and elicited RSV-A and RSV-B nAb responses noninferior to those observed in older adults in the pivotal study, supporting inference of efficacy in this population.

Spatiotemporal Association of Coronavirus Disease 2019 Cases and Deaths With Exposure to Wildfire Particulate Matter in 2020
Authors state, ‘Climate change is anticipated to have profound effects on human health, including in infectious diseases. Wildfires have been increasing in frequency and intensity due to climate change and have been linked to worsening respiratory disease outcomes. We aimed to demonstrate whether there was an association between wildfire smoke and coronavirus disease 2019 (COVID-19) in California during 2020.’ They looked into associations between wildfire smoke, measured as particulate matter, and COVID-19 cases and deaths at the county level in California in 2020. They found a one-month lag increase of 203 COVID-19 cases per 10 000 persons per 10 µg/m3 of smoke exposure (P < .001) at the county level. There was a one-month lag increase of 2.75 COVID-19 deaths per 10 000 persons per 10 µg/m3 of smoke exposure (P < .001) at the county level. It appeared that wildfire smoke exposure likely increased the spread of COVID-19 and worsened the mortality rate.