Presence of Elevated Interleukin – 6 (IL-6) in the Blood of COVID-19 Convalescent Patients (40 – 93 Days) Post Onset of Symptoms Could be an Indicator of Ongoing Activation of the Immune System

Abstract

IL-6 concentrations rise with the onset of COVID-19 infection and is detected in 68% of patients on admission but is expected to reduce after the acute phase. IL-6 concentrations at time points: (2-7 days), (6-11 days), (11-15 days) and (13-20 days) after intensive care unit (ICU) admission showed the highest level of IL-6 concentrations at time point 2-7 days, we decided to characterize IL-6 concentrations in serum samples collected in the sera of COVID-19 convalescent patients (40 – 93 days) post onset of symptoms. The estimated IL- 6 concentrations detected ranged between 2.65 pg/ml and 29.01 pg/ml, with a median of 9.18 pg/ml. Nine out of the 28 (32.14%) patients had normal IL-6 levels (<7 pg/ml) and 19 of the 28 patients (68%) had IL-6 elevated concentrations (>7 pg/ml). The IL-6 concentrations were grouped normal (<7 pg.ml, n= 9), mildly elevated (7 – 10 pg/ml, n = 10) and elevated (>10 pg/ml n = 9). There was no relationship between IL-6 concentrations with gender, days from onset of symptoms, days from subsiding symptoms and COVID-19 IgG antibodies. There was some relationship with age, as the younger patient cohort produced much higher IL-6 concentrations than the older patient cohort. This study describes an increase in blood IL-6 concentrations in the sera of COVID-19 convalescent patients (40 – 93 days) post onset of symptoms like that seen in COVID patients on admission and higher levels seen in the younger patient cohort indicating that “cytokine storms” still occur in the recovery phase.