So very true! COVID 19 is like Forrest Gump's box of chocolates, "You never know what you are going to get!" We do know that with certain comorbidities and advanced age you are more likely to get some consequences, but this is not a hard and fast rule granting immunity to those potential victims that are younger or uncompromised.
The most common cause of death in cases has been the exaggerated and unpredictable immune system response. This occurs with some individuals where the lungs are attacked initially and the resulting cytokine storm results in massive inflammation and tissue damage with the patient either choking to death because the normal oxygen/CO 2 exchange is compromised by fluid and exudate in the alveolae or damage to those same tissues is so great that the exchange is permanently diminished to a level where life is an unsustainable proposition. Even if you survive with capacity above that level you can end up with an ARDS like condition where, depending on the extent of the residuals, your pulmonary function is so compromised you can't function in any situation requiring significant physical exertion and you may need constant oxygen augmentation. One poster mentioned a friend that recovered, but now has similar residuals.
The virus can attack other vital systems in the body and cause damage to them as well. We have heard the horror stories involving the brain, the digestive system, and the renal function. . There are the disturbing cases where the circulatory systems of some younger individuals have experienced a similar immune response similar to the pulmonary cases where excessive inflammation of the blood vessels has resulted in death or damage to other organs. Similar to Kawasaki Disease.
Perhaps the second greatest killer is the often observed condition of hypercoagulability that can accompany the infection and can result in the clotting of blood in the vital organs like the heart, brain, and lungs. When patients are immobilized and confined to a bed while on a ventilator you end up a most undesirable convergence and you have the setting for a perfect storm. Translated, that might mean a stroke, an MI, or a pulmonary embolism that kills the patient. How long does this clotting threat continue? Some patients are taking weeks and even months to fight off the virus and get over some of their symptoms. Another poster stated that a friend "dropped dead". No cause of death is provided, but this could easily be a situation where the hypercoagulability is responsible.
Since this disease is new and has not mirrored precisely the known histories of the two previous Corona viruses that carried serious consequences for humans, SARS and MERS, there is a lot of research to be done and a lot of data to be collected. The fact that a lot of research on vaccines for those two viruses had already been ongoing for some time offers the hope for an early vaccine for this version. Any conclusions about COVID 19 this early in the process carry significant questions regarding validity simply due to the definition of validity. Those conclusions or theories may ultimately be proven correct, but based on limited populations or anecdotal stories they must be treated with some skepticism. The hydroxychloroquine debacle is a classic illustration. We know that some patients with autoimmune conditions respond favorably and so there was some hope that in patients experiencing the overblown immune response there might be some type of benefit. Turns out that the number getting benefits is too small to register as "significant" in the limited studies that are available. The infrequent but potentially lethal side effects related to cardiac arrhythmias was known in cases of both malaria and autoimmune use. Since the only study showing elevated risk of this complication in SARS2 cases has been retracted by the presenting cardiologists at Brigham in Boston, there is now no valid study supporting that conclusion. There are about 14 studies indicating no significant therapeutic benefits to counter the French study. Even if there was some benefit in those cases presenting with inflammatory response issues there is no study showing that the hypercoagulability concerns are improved.
The British now have a study, subject to the same limitations on validity, that say a simple steroid has improved the survival outcomes for the exaggerated immune response cases by about 30%.
The Remedivir studies show some success in limiting the extent of the virus' impact by interfering with the replication process. Apparently slowing the progression of the infection allows the immune system to get into action in a less drastic fashion in some that might otherwise experience that counter productive exaggerated rush.
Bottom line is that there is a lot of research to be done on treatment protocols, medications to limit or eliminate the known complications, and development of that elusive vaccine.