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Due to theoretical and practical applications in biomedical, environmental, and industrial microbiology, robust metrics for quantifying the virulence of pathogens is vital. For many virus–host systems, multiple virus strains propagate through host populations. Each strain may exhibit a different virulence level. Likewise, different hosts may manifest different levels of host resilience to infection by a given virus. Recent publications have assessed metrics for quantifying virulence (VR) from growth curve data. Regardless of the metric used, a feature that most methods have in common is focus on the exponential growth phase of virus–host interactions. Often ignored is mortality phase. Following a report introducing the Stacy–Ceballos Inhibition Index (ISC), a robust metric to quantify relative virulence (VR) between viruses, we have turned attention to quantifying relative resilience (RR) between hosts in single-virus/single-host (SVSH) experimental infections. Although resilience during viral infection impacts the entire host growth curve, RR has particular biological significance during the mortality phase. In this report, we argue that calculating RR using a modified ISC provides a robust metric for comparisons between SVSH infections. Wet lab data from fusellovirus infections in Sulfolobales, bacteriophage infections in Mycobacteriales, and simulated infected-host growth profiles form the basis for developing this metric, RR, for quantifying resilience. 

Abstract Fractional Chern insulators (FCIs) are lattice analogues of fractional quantum Hall states that may provide a new avenue towards manipulating non-Abelian excitations. Early theoretical studies 1–7 have predicted their existence in systems with flat Chern bands and highlighted the critical role of a particular quantum geometry. However, FCI states have been observed only in Bernal-stacked bilayer graphene (BLG) aligned with hexagonal boron nitride (hBN) 8 , in which a very large magnetic field is responsible for the existence of the Chern bands, precluding the realization of FCIs at zero field. By contrast, magic-angle twisted BLG 9–12 supports flat Chern bands at zero magnetic field 13–17 , and therefore offers a promising route towards stabilizing zero-field FCIs. Here we report the observation of eight FCI states at low magnetic field in magic-angle twisted BLG enabled by high-resolution local compressibility measurements. The first of these states emerge at 5 T, and their appearance is accompanied by the simultaneous disappearance of nearby topologically trivial charge density wave states. We demonstrate that, unlike the case of the BLG/hBN platform, the principal role of the weak magnetic field is merely to redistribute the Berry curvature of the native Chern bands and thereby realize a quantum geometry favourable for the emergence of FCIs. Our findings strongly suggest that FCIs may be realized at zero magnetic field and pave the way for the exploration and manipulation of anyonic excitations in flat moiré Chern bands.