posted by RITA .
The 1918 Influenza Epidemic was the worse one on record. People infected early in the epidemic had a mild flu, while those later infected had a much more severe form of the disease. What is the explanation for this observation and what laboratory studies mimic these results? Why do you think this doesn’t occur for all infectious diseases?
You will have to search for lab studies, I don't know them.
The Flu 1918 mutated, the mutation was much more deadly. The folks who had already had the original version were largely immune from this mutation, however, the new mutation now struck elderly and children, and killed them (mainly from pneumonia).