Finding evidence for treatment decisions in a pandemic

Tixagevimab/cilgavimab for preventing COVID-19 during the Omicron surge: retrospective analysis of National Veterans Health Administration electronic data

Little is known regarding the effectiveness of tixagevimab/cilgavimab in preventing SARS-CoV-2 infection in vaccinated immunocompromised patients, particularly after the emergence of the Omicron variant. In this retrospective cohort study with exact matching and propensity score adjustment within the U.S. Department of Veterans Affairs (VA) healthcare system, we selected immunocompromised veterans age ≥18 years as of 1 January 2022, receiving VA healthcare. We compared a cohort of 1,878 patients treated with at least one dose of intramuscular tixagevimab/cilgavimab to 7,014 matched controls selected from patients who met study criteria but were not treated. Patients were followed through 15 June 2022, or until death, whichever occurred earlier. The primary outcome was a composite of SARS-CoV-2 infection, COVID-19-related hospitalization, and all-cause mortality. We used Cox proportional hazards modeling to estimate the hazard ratios (HRs) and 95% CI for the association between receipt of tixagevimab/cilgavimab and outcomes. Most (73%) tixagevimab/cilgavimab recipients were ≥65 years old, and 80% had ≥3 mRNA vaccine doses or two doses of Ad26.COV2. Compared to matched controls, recipients had a lower incidence of the composite COVID-19 outcome (49/1,878 [2.6%] versus 312/7,014 [4.4%]; HR 0.35; 95% CI, 0.24-0.52), and individually SARS-CoV-2 infection (HR 0.44; 95% CI, 0.22-0.88), COVID-19 hospitalization (HR 0.24; 95% CI, 0.10-0.59), and all-cause mortality (HR 0.32; 95% CI, 0.19-0.55). In conclusion, tixagevimab/cilgavimab was associated with lower rates of SARS-CoV-2 infection and severe COVID-19 during the Omicron BA.1, BA.2, and BA.2.12.1 surge. IMPORTANCE SARS-CoV-2 remains an ongoing global health crisis that justifies continued efforts to validate and expand, when possible, knowledge on the efficacy of available vaccines and treatments. Clinical trials have been limited due to fast tracking of medications for mitigation of the COVID-19 pandemic for the general population. We present a real-world analysis, using electronic health record data, of the effectiveness of tixagevimab/cilgavimab for the prevention of COVID-19 infection in the unique population of U.S. veterans. Unlike those in the PROVENT clinical trial from which the emergency use authorization for tixagevimab/cilgavimab as a preventative treatment arose, the veterans population is highly immunocompromised and nearly 96% totally vaccinated. These demographics allowed us to analyze the effectiveness of tixagevimab/cilgavimab in preventing COVID-19 under different conditions in a more fragile population than that of the initial clinical trial.

Exercise and Experiments of Nature

In this article, we highlight the contributions of passive experiments that address important exercise-related questions in integrative physiology and medicine. Passive experiments differ from active experiments in that passive experiments involve limited or no active intervention to generate observations and test hypotheses. Experiments of nature and natural experiments are two types of passive experiments. Experiments of nature include research participants with rare genetic or acquired conditions that facilitate exploration of specific physiological mechanisms. In this way, experiments of nature are parallel to classical "knockout" animal models among human research participants. Natural experiments are gleaned from data sets that allow population-based questions to be addressed. An advantage of both types of passive experiments is that more extreme and/or prolonged exposures to physiological and behavioral stimuli are possible in humans. In this article, we discuss a number of key passive experiments that have generated foundational medical knowledge or mechanistic physiological insights related to exercise. Both natural experiments and experiments of nature will be essential to generate and test hypotheses about the limits of human adaptability to stressors like exercise. © 2023 American Physiological Society. Compr Physiol 13:4879-4907, 2023.