Daily Respiratory Research Analysis

Neutrophils play key protective roles in influenza infections, yet excessive neutrophilic inflammation is a hallmark of acute lung injury during severe infections. Phenotypic heterogeneity is increasingly recognized in neutrophil populations; however, how functional variation in neutrophils between individuals determine the diverse outcomes of influenza remains unclear. To examine immunologic responses that may drive varying outcomes in influenza, we infected C57BL/6 (B6) and A/J mice with mouse-adapted influenza A virus A/PR/8/34 H1N1. A self-resolving dose in B6 mice was lethal in A/J mice, which had increased viral load throughout infection accompanied by prominent bronchoalveolar neutrophilia and pulmonary vascular leakage preceding mortality. Notably, the B6 mice heavily recruited neutrophils to lungs early in infection while A/J mice failed to do so. Neutrophils from A/J mice additionally displayed reduced neutrophil extracellular trap (NET) release and reactive oxygen species (ROS) generation compared to B6 mice early in infection, suggesting the failure to control virus in A/J mice was a product of deficient neutrophil response. To determine if variation in neutrophils between strains governed viral control and inflammation, we adoptively transferred bone marrow neutrophils from B6 or A/J donors to A/J recipients early in infection and found that the transfer of B6 neutrophils enhanced viral clearance and abrogated the dissemination of CXCL1 and IL-6. The transfer of A/J neutrophils, however, failed to achieve either. Furthermore, B6 neutrophils were capable of greater levels of viral killing in vitro than their A/J counterparts. These results suggest that a key moderator of inflammation in influenza infection is the control of virus by neutrophils early in infection. Thus, host-specific differences in both the recruitment of these cells as well as interindividual variation in neutrophil ability to support viral clearance may in part dictate differing susceptibility to respiratory viral infections.

BACKGROUND: Nirmatrelvir with ritonavir (Paxlovid) is indicated for patients with Coronavirus Disease 2019 (COVID-19) who are at risk for progression to severe disease due to the presence of one or more risk factors. Millions of treatment courses have been prescribed in the United States alone. Paxlovid was highly effective at preventing hospitalization and death in clinical trials. Several studies have found a protective association in real-world data, but they variously used less recent study periods, correlational methods, and small, local cohorts. Their estimates also varied widely. The real-world effectiveness of Paxlovid remains uncertain, and it is unknown whether its effect is homogeneous across demographic strata. This study leverages electronic health record data in the National COVID Cohort Collaborative's (N3C) repository to investigate disparities in Paxlovid treatment and to emulate a target trial assessing its effectiveness in reducing severe COVID-19 outcomes. METHODS AND FINDINGS: This target trial emulation used a cohort of 703,647 patients with COVID-19 seen at 34 clinical sites across the United States between April 1, 2022 and August 28, 2023. Treatment was defined as receipt of a Paxlovid prescription within 5 days of the patient's COVID-19 index date (positive test or diagnosis). To emulate randomization, we used the clone-censor-weight technique with inverse probability of censoring weights to balance a set of covariates including sex, age, race and ethnicity, comorbidities, community well-being index (CWBI), prior healthcare utilization, month of COVID-19 index, and site of care provision. The primary outcome was hospitalization; death was a secondary outcome. We estimated that Paxlovid reduced the risk of hospitalization by 39% (95% confidence interval (CI) [36%, 41%]; p < 0.001), with an absolute risk reduction of 0.9 percentage points (95% CI [0.9, 1.0]; p < 0.001), and reduced the risk of death by 61% (95% CI [55%, 67%]; p < 0.001), with an absolute risk reduction of 0.2 percentage points (95% CI [0.1, 0.2]; p < 0.001). We also conducted stratified analyses by vaccination status and age group. Absolute risk reduction for hospitalization was similar among patients that were vaccinated and unvaccinate, but was much greater among patients aged 65+ years than among younger patients. We observed disparities in Paxlovid treatment, with lower rates among black and Hispanic or Latino patients, and within socially vulnerable communities. This study's main limitation is that it estimates causal effects using observational data and could be biased by unmeasured confounding. CONCLUSIONS: In this study of Paxlovid's real-world effectiveness, we observed that Paxlovid is effective at preventing hospitalization and death, including among vaccinated patients, and particularly among older patients. This remains true in the era of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Omicron subvariants. However, disparities in Paxlovid treatment rates imply that the benefit of Paxlovid's effectiveness is not equitably distributed.

BACKGROUND: In Catalonia, infants <6 months old were eligible to receive nirsevimab, a novel monoclonal antibody against respiratory syncytial virus (RSV). We aimed to analyze nirsevimab's effectiveness in hospital-related outcomes of the seasonal cohort (born during the RSV epidemic from October to January 2024) and compared them with the catch-up cohort (born from April to September 2023). METHODS: Retrospective cohort study of all infants born between October 1, 2023, and January 21, 2024, according to their immunization with nirsevimab (immunized and nonimmunized). We followed individuals until the earliest of an outcome-hospital emergency visits, hospital admission or pediatric intensive care unit (PICU) admission due to RSV-associated or all-causes bronchiolitis-death or the end of the study. We used the Kaplan-Meier estimator and fitted Cox regression models using a calendar time scale to estimate hazard ratios (HRs) and their 95% confidence interval (CI). Sensitivity analysis was performed through matching. RESULTS: Among 15,341 infants, a dose of nirsevimab led to an adjusted HR for hospital admission, PICU admission and emergency visits due to RSV bronchiolitis of 0.26 (95% CI: 0.17-0.39), 0.15 (95% CI: 0.07-0.28) and 0.46 (95% CI: 0.23-0.90), respectively. For all-causes bronchiolitis, the former adjusted HRs were 0.45 (95% CI: 0.31-0.63), 0.23 (95% CI: 0.13-0.41) and 0.49 (95% CI: 0.35-0.68), respectively. CONCLUSIONS: Nirsevimab was associated with reductions of 74% and 85% hospitalizations and PICU admissions regarding RSV-associated bronchiolitis, respectively. These percentages are slightly lower than those for the catch-up cohort. This information may help the implementation of RSV-immunization campaigns by public health authorities.