Final answer:
The 1918 influenza pandemic, caused by an antigenic shift creating a new H1N1 virus, resulted in high mortality rates, especially among young adults, and significantly impacted society during World War I due to rapid troop movements and crowded conditions. Misnamed the 'Spanish Flu,' it had far-reaching economic and health consequences worldwide.
Step-by-step explanation:
The 1918 strain of influenza, also known as the Spanish Flu, was distinct from previous strains due to a variety of factors. An antigenic shift likely resulting from the recombination of avian and human viruses created a new H1N1 virus. This strain was especially lethal and had the ability to rapidly spread worldwide, claiming the lives of an estimated 40 to 50 million people, which was more than double the number of fatalities in World War I.
The virus proved unique in causing high mortality rates among young adults, aged eighteen to thirty-five, rather than the very young or very old, which is more typical in influenza outbreaks. Additionally, conditions such as crowding, poor sanitation, and the rapid mobilization of troops during World War I facilitated the virus's dissemination. The flu also caused severe economic impacts, as it led to shutdowns in mines, reduced services, and overwhelmed healthcare and burial services.
Interestingly, the strain was misnamed 'Spanish Influenza' because reports of the disease first gained attention in the uncensored newspapers of neutral Spain. The 1918 influenza pandemic profoundly affected military and civilian populations alike and was a significant event of the early 20th century, demonstrating the catastrophic potential of infectious diseases.