A cytokine storm is an overreaction by an immune response such that it releases too many cytokines than are beneficial. This can cause a fatal inflammatory reaction. The necessity for early treatment of COVID-19 -- rather than a "wait and see" approach -- is to advert a deadly cytokine storm.
Some have suspected that a cytokine storm, which hits starting around day 3 of the progression of COVID-19, is what causes its high mortality. It is characterized by:
- low oxygen levels observable by pulse oximeters, which is why ventilators are used but often do not actually save the patients' lives
- high fever (more than 103 degrees)
- low blood pressure
- a white cell count at 2,000 when it should be between 4.5 and 10.
- lymphocytes, which fight a virus, at 200 when they should be between 1000 and 1,500 — they were under 200.
- low platelet count, such as 100,000
Others dispute that a cytokine storm occurs worse in COVID-19.