Self-collected finger-prick blood for gene expression profiling: Unveiling early immune responses in mild COVID-19.

Whole-blood gene expression analysis is essential for understanding molecular host responses, yet its use typically relies on venous sampling, limiting feasibility for frequent and remote monitoring. In an ancillary study of the COVERAGE France platform trial (NCT04356495), which enrolled at-risk outpatients with mild coronavirus disease 2019 (COVID-19) monitored at home, we compared transcriptomic profiles obtained from paired venous blood (Tempus tubes) and ultralow-volume, self-collected finger-prick capillary samples. We observed moderate to good concordance at the individual gene level and excellent agreement at the gene-set level between the two sampling approaches. High-frequency finger-prick sampling enabled daily resolution of immune dynamics, revealing early interferon responses, sustained neutrophil activation, and evolving erythroid and inflammatory signatures during the initial phase of mild COVID-19. These results demonstrate that finger-prick sampling is a feasible and reliable approach for at-home transcriptomic profiling, offering a powerful tool for longitudinal immune monitoring and advanced clinical research.