A number of factors influence the way the virulence of a virus — that is, how harmful it is to its host — affects its ability to survive and spread; in some cases, higher virulence may help a virus survive and spread.
Many viruses have evolved to become more lethal over time.
As scientists work to uncover the characteristics of recently discovered COVID-19 variant omicron, social media posts are claiming that it represents a diminished risk to the public.
"Pathogens evolve to become less, not more, virulent over time," says one Facebook post. "If pathogens evolved to become more virulent with time they’d destroy their hosts which they depend on to live and you wouldn’t be here to read this." The post cites HIV in Uganda and Ebola as examples of viruses that have become less virulent with time.
This post was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)
The claim makes a broad generalization about pathogens that’s not supported by science. It has been well-documented that pathogens can evolve to be more virulent. And many viruses, including HIV and Ebola, have in fact become more lethal over time.
"You can’t just say it’s going to become nicer — that somehow a well-adapted pathogen doesn’t harm its host," Andrew Read, an evolutionary microbiologist at Penn State University, said in an interview. "Modern evolutionary biology, and a lot of data,...
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