6. The second wave of Spanish Flu did not affect most survivors of the first wave
When the second wave of Spanish Flu hit in the autumn of 1918, in a far more virulent and deadly form of the virus, doctors around the world noted that those who had contracted the disease earlier were not susceptible to the virus. That indicated that the virus was the same which had struck earlier, though it had mutated into a stronger form, and the first wave had in effect inoculated those struck by the disease. Studies conducted since the pandemic demonstrate that the virus was strengthened by the circumstances of the First World War. The theory of natural selection was demonstrated by the spread of the disease during the first wave. At that time soldiers in the camps and trenches which were not severely ill remained where they were, while the very sick were packed together in trains and hospitals.
Crowding the seriously ill together allowed the virus which had sickened them to strengthen, and when it reappeared in the second wave it was much stronger than that of the first. When the second wave hit it caused the same result in victims as the first, an overly strong response of the body’s autoimmune system to kill the virus. Since the virus was stronger than its predecessor the response was as well. Young, previously healthy men with healthy immune systems were thus more susceptible to both contracting the virus and experiencing an aggressive autoimmune response (a cytokine storm), which led to their deaths from the direct consequences of the flu, or secondary causes such as pneumonia.