https://en.wikipedia.org/wiki/Marek%27s_disease#Prevention https://en.wikipedia.org/wiki/Marek%27s_disease#Prevention is the canonical example: "However, the l

https://en.wikipedia.org/wiki/Marek%27s_disease#Prevention https://en.wikipedia.org/wiki/Marek%27s_disease#Prevention is the canonical example: "However, the leaky vaccine changes this evolutionary pressure and permits the evolution of highly virulent strains. The vaccine's inability to prevent infection and transmission allows the spread of highly virulent strains among vaccinated chickens. The fitness of the more virulent strains is increased by the vaccine." See: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516275/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516275/ Andrew Read on the issue: https://theconversation.com/vaccines-could-affect-how-the-coronavirus-evolves-but-thats-no-reason-to-skip-your-shot-165960 https://theconversation.com/vaccines-could-affect-how-the-co...