Background: The virological and immunological effects of the immunomodulatory drugs used for COVID-19 remain unknown . We evaluated the impact of interleukin (IL) -6 blockade with tocilizumab on SARS-CoV-2 viral kinetics and the antibody response in patients with COVID-19 .
Methods: Prospective cohort study in patients admitted with COVID-19 . Serial nasopharyngeal and plasma samples were measured for SARS-CoV-2 RNA and S-IgG/N-IgG titers, respectively . Findings: 138 patients with confirmed infection were included; 76 (55 %) underwent IL-6 blockade . Median initial SOFA (p = 0•016) and SARS-CoV-2 viral load (p <0•001, Mann-Whitney-Wilcoxon test) were significantly higher among anti-IL-6 users . Patients under IL-6 blockade showed delayed viral clearance in the Kaplan-Meier curves (HR 0•35 [95% CI] [0•15–0•81], log-rank p = 0•014), but an adjusted propensity score matching model did not demonstrate a significant relationship of IL-6 blockade with viral clearance (HR 1•63 [0•35–7•7] ). Cox regression showed an inverse association between SARS-CoV-2 RNA clearance and the initial viral load (HR 0•35 [0•11–0•89] ). Patients under the IL-6 blocker showed shorter median time to seropositivity, higher peak antibody titers, and higher cumulative proportion of seropositivity in the Kaplan Meier curves (HR 3•1 [1•9–5] for S-IgG; and HR 3•0 [1•9–4•9] for N-IgG; log-rank p <0•001 for both). However, no significant differences between groups were found in either S-IgG (HR 1•56 [0•41–6•0] ) nor N-IgG (HR 0•96 [0•26–3•5] ) responses in an adjusted propensity score analysis . Interpretation: Our results suggest that in patients infected with SARS-CoV-2, IL-6 blockade does not impair the viral specific antibody responses . Although a delayed viral clearance was observed, it was driven by a higher initial viral load . The study supports the safety of this therapy in patients with COVID-19. Funding: Instituto de salud Carlos III (Spain).