Publication date: Oct 10, 2024

The first Adaptive COVID-19 Treatment Trial (ACTT-1) showed that remdesivir improved COVID-19 recovery time compared with placebo in hospitalized adults. The secondary outcome of mortality was almost significant overall (p = 0. 07) and highly significant for people receiving supplemental oxygen at enrollment (p = 0. 002), suggesting a mortality benefit concentrated in this group. We explore analysis methods that are helpful when a single subgroup benefits from treatment and apply them to ACTT-1, using baseline oxygen use to define subgroups. We consider two questions: (1) is the remdesivir effect for people receiving supplemental oxygen real, and (2) does this effect differ from the overall effect? For Question 1, we apply a Bonferroni adjustment to subgroup-specific hypothesis tests and the Westfall and Young permutation test, which is valid when small cell counts preclude normally distributed test statistics (a frequently unexamined condition in subgroup analyses). For Question 2, we introduce Q, the largest standardized difference between subgroup-specific effects and the overall effect. Q simultaneously tests whether any subgroup effect differs from the overall effect and identifies the subgroup benefitting most. We demonstrate that Q strongly controls the familywise error rate (FWER) when test statistics are normally distributed with no mean-variance relationship. We compare Q to a related permutation test, SEAMOS, which was previously proposed but not extensively applied or tested. We show that SEAMOS can have inflated Type 1 error under the global null when control arm event rates differ between subgroups. Our results support a mortality benefit from remdesivir in people receiving supplemental oxygen.

Semantics

Original Article