Early differences in cytokine production distinguish severity of COVID-19.

Most COVID-19 patients experience asymptomatic/mild symptoms, but some suffer critical symptoms requiring intensive care. It is important to determine how asymptomatic/mild patients react to SARS-CoV-2 infection and suppress virus spread. Innate immunity is important for evasion from the first virus attack, and it may play an important role in the pathogenesis in these patients. We measured serum cytokine levels of 95 COVID-19 patients during the infection's acute phase and are first to report that significantly higher IL-12 and IL-2 levels were induced in asymptomatic/mild patients versus those in the moderate/severe patients, indicating these cytokines' key roles in asymptomatic/mild infections' pathogenesis.