Minimal impact of ivermectin on immune response and transcriptional profiles in naïve adults with mild COVID-19

Ivermectin (IVM), an antiparasitic drug, was repurposed to treat COVID-19 based on its in vitro antiviral effects. However, it was abandoned after multiple clinical trials reported a lack of efficacy. Immunomodulatory effects have been proposed but remain unclear, yet they may be relevant given IVM use for other infections. We assessed the IVM immunomodulatory effect in 24 participants from a clinical trial evaluating its potential to reduce COVID-19 transmission in mild cases within 48 hours of symptoms onset. The IVM-treated patients showed non-significant lower viral loads, and a significantly shorter duration of hyposmia/anosmia. We measured IgG, IgA, and IgM against five SARS-CoV-2 antigens, and 30 cytokines by Luminex, alongside whole blood RNA sequencing, pan-leukocyte immunophenotyping, and SARS-CoV-2-specific T cell analysis by flow cytometry from day 1 to day 28 post-treatment. All antibody responses increased from day 4, while 13 cytokines significantly decreased over time (adjusted p<0.05). IVM-treated patients had only significantly higher anti-nucleocapsid IgG levels at day 4 (adjusted p=0.041) and 7 (adjusted p=0.045) compared to placebo. SARS-CoV-2-specific CD4+ and CD8+ T cells increased over time, with significantly higher effector memory CD4+ T cells at day 7 compared to day 1 (p=0.027) and the only difference between groups was lower frequencies of spike-specific naïve CD4+ T cells at day 7 in IVM-treated participants (0.006% vs 0.036% p=0.02). Transcriptomic data showed downregulation of innate and antiviral blood transcriptional modules (BTMs) over time, with an increase in adaptive immune related BTMs. While no differential gene expression was detected, the IVM-treated had upregulated innate and downregulated T cell and cell cycle BTMs compared to placebo. Overall, our comprehensive longitudinal analysis of early immune responses in mild COVID-19 revealed no robust immunological effects of IVM, consistent with clinical trials results and suggesting a lack of efficacy of IVM in COVID-19 treatment.