History Suggests New Omicron Variant Is Likely Even More Mild: the law of declining virulence

by Mike Mutzel


Let’s review a the long-known law of declining virulence which describes how viruses and parasites evolve to become less virulent over time as they infect more hosts.



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Brüssow, H. (2021). What we can learn from the dynamics of the 1889 “Russian flu” pandemic for the future trajectory of COVID-19. Microbial Biotechnology, 14(6), 2244–2253.


Sciences, P. M. H. A. P. O. T. L.,. (2012). Why do Parasites Harm Their Host? On the Origin and Legacy of Theobald Smith's‘ Law of Declining Virulence’—1900-1980. Jstor

Gaeta, G. (2021, September 19). Mass vaccination in a roaring pandemic.

Mass vaccination produces a reduction in virus circulation, but also evolutive pressure towards the appearance of virus-resistant strains. We discuss the balance between these two effects, in particular when the mass vaccination takes place in the middle of an epidemic period.

Alizon, S., & Sofonea, M. T. (2021). SARS-CoV-2 virulence evolution: Avirulence theory, immunity and trade-offs. Journal of Evolutionary Biology. 



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