Within a few years, the influenza strain behind the 1918 pandemic became less life threatening.
Dr. Keith Armitage, a professor of medicine in the division of infectious diseases at Case Western Reserve University, says this is likely due to a combination of herd immunity and the virus mutating to produce a less severe illness.
The 1918 influenza strain never disappeared, rather it continued to mutate and a version of it continues to circulate to this day.
“If you think about the way viruses behave, biologically, their reason for living is to replicate and spread, and there’s really no advantage for the virus to kill the host,” said Armitage.
What a virus wants to do is infect a host and be contagious so it can infect another host and it can continue to spread.
As part of this process, respiratory viruses often mutate and become less virulent and therefore less of a serious health issue.