Although most symptoms of the virus are light, the real danger is in how fast it spreads and affects people. Physical contact is the leading cause of its spread, so avoid public gatherings and social events. In extreme cases, the CDC reports that the virus can cause pneumonia, respiratory failure, septic shock, and then death in sick people. Most of the COVID-19 complications are caused by cytokine release syndrome or a cytokine storm. An infection causes your immune system to flood your blood with inflammatory proteins called cytokines. They can kill tissue and damage your organs.