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Nothing completely prevents infection, but vaccines are the best way to mitigate it.

• hh3k0 5y ago
  > Under normal conditions, highly virulent strains of the virus are not selected. A highly virulent strain would kill the host before the virus would have an opportunity to transmit to other potential hosts and replicate. Thus, less virulent strains are selected. These strains are virulent enough to induce symptoms but not enough to kill the host, allowing further transmission. However, the leaky vaccine changes this evolutionary pressure and permits the evolution of highly virulent strains.[13] 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. https://en.wikipedia.org/wiki/Marek%27s_disease#Prevention https://en.wikipedia.org/wiki/Marek%27s_disease#Prevention
  • saalweachter 5y ago
    Following the references, it all seems solid; the referenced authors note this hasn't been observed for human viruses yet (2017), but posits non-sterilizing vaccines in humans might be too new. On the other hand, it seems like a kind of inverse prisoners' dilemma. If no one vaccinates, this particular pathway for the evolution of super-viruses is closed (although others remain open). If some people vaccinate, and a super-virus evolves, they're fine and the rest are screwed, classic P.D. But it deviates where unlike the classic P.D. where things get worse if everyone defects, once everyone vaccinates, it doesn't matter if a super-virus evolves, because everyone is protected. So while this raises an interesting policy question on whether non-sterilizing vaccines are worth the risk, once people begin "defecting" by getting vaccinated, it seems like a bad move to risk staying unvaccinated yourself.