Daily viral kinetics and innate and adaptive immune responses assessment in COVID-19: a case series

Background Viral shedding patterns and its correlation with the immune responses of mildly symptomatic COVID-19 patients are still poorly characterized. Methods: We enrolled the first five COVID-19 patients quarantined in our institution; none received immunomodulatory treatment. We monitored shedding of viral RNA and infectious virus by RT-PCR and cell culture from the upper respiratory tract, and characterized the kinetics of systemic innate and adaptive immune responses. Results Despite mild clinical disease, high viral loads and shedding of infectious virus were observed from the respiratory tract, with isolation of infectious virus and prolonged positivity by PCR up to day 7 and 19 post onset of symptoms, respectively. Robust innate responses characterized by an increase in activated CD14+CD16+ monocytes and cytokine responses were observed as early as 2 days after symptoms onset. Cellular and humoral SARS-CoV-2 specific adaptive responses were detectable in all patients. Conclusion Infectious virus shedding was limited to the first week of symptom onset in mild cases. A strong innate response, characterized by the mobilization of activated monocytes during the first days of infection, as well as SARS-CoV-2 specific antibodies were detectable, even in patients with mild disease.