4 ms·

Keep in mind that imperfect vaccination shifts this triad in the direction of higher sustainable lethality: https://en.wikipedia.org/wiki/Marek's_disease https:

Keep in mind that imperfect vaccination shifts this triad in the direction of higher sustainable lethality: https://en.wikipedia.org/wiki/Marek's_disease https://en.wikipedia.org/wiki/Marek's_disease In both the natural and leaky-vaccine scenarios, the virus evolves towards an ecological equilibrium, but in the leaky-vaccine scenario, that equilibrium is shifted in the direction of greater lethality. See the linked article: as a direct consequence of mass vaccination of chickens, Marek's diseased evolved from a minor illness into a highly-virulent, highly-transmissible disease that causes 100% lethal cancer in chickens unless the chicks are vaccinated before they hatch from their eggs.

jl6 5y ago
What do you think about this article, by the author of the Marek’s disease study, that criticizes extrapolating from the chicken scenario to the covid scenario?: https://theconversation.com/amp/vaccines-could-affect-how-the-coronavirus-evolves-but-thats-no-reason-to-skip-your-shot-165960 https://theconversation.com/amp/vaccines-could-affect-how-th...
- angelzen 5y ago
  The core argument is that Marek kills in 10 days or less, which is too soon for viral spread to happen. MDV vaccines keep chickens from dying, thus spread of hot variants can occur. Since covid doesn't kill that much, Marek phenomenon can't happen. The obvious issue with the argument is that the hot lethal variants are observed post vaccine availability. Earlier strains were "mild" or "virulent", but not "very virulent plus". "Death was relatively rare". From an 1998 article on Marek, there appear to have been at least 3 jumps in Marek virulence, one in the late '50s pre vaccines (mild => virulent) and two post vaccine availability (virulent => very virulent, very virulent => very virulent plus), see chart on page S50. https://www.tandfonline.com/doi/pdf/10.1080/03079459808419292 https://www.tandfonline.com/doi/pdf/10.1080/0307945980841929... From Andrew Read's own 2015 article: "MDV became increasingly virulent over the second half of the 20th century [19,21–24]. Until the 1950s, strains of MDV circulating on poultry farms caused a mildly paralytic disease, with lesions largely restricted to peripheral nervous tissue. Death was relatively rare. Today, hyperpathogenic strains are present worldwide. These strains induce lymphomas in a wide range of organs and mortality rates of up to 100% in unvaccinated birds." https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002198 https://journals.plos.org/plosbiology/article?id=10.1371/jou... The conclusion of the rebuttal article you linked to is rather terrifying. If there ever was a "the road to [chicken] Hell is paved with good intentions", this is it. "In the history of human and animal vaccines, there have not been many cases of vaccine-driven evolution. But in every one of them, individuals and populations have always been better off when vaccinated. At every point in the 50-year history of vaccination against Marek’s disease, an individual chicken exposed to the virus was healthier if it was vaccinated."
  - jl6 5y ago
    > The obvious issue with the argument is that the hot lethal variants are observed post vaccine availability. But is that true? Which hot lethal variants arose post vaccine availability?
    - angelzen 5y ago
      From 1998 https://www.tandfonline.com/doi/pdf/10.1080/03079459808419292 https://www.tandfonline.com/doi/pdf/10.1080/0307945980841929..., page S50, Figure 4: BIVAL vv (late 70s) then RISPENS vv+ (early 90s). The text: "The three major pathotype shifts are: (1) from m MDV to v MDV strains in the late 1950s; (2) from v MDV to vv MDV in the late 1970s; (3) the appearance of the putative vv + pathotype in the early 1990s (Figure 4). Each occurrence has been associated with greater disease losses which have persisted until introduction of the next generation of vaccine. The reason for the shifts remain speculative. Shifts in the 1970s and 1990s may have been in response to certain MD vaccines. Kreager (1996) has suggested vaccines may have only a 10-year useful life before new strains evolve. The shift in the 1950s occurred prior to vaccine use, but may have been related to changes in poultry husbandry, especially the move towards larger houses and the increasing density of poultry operations in certain geographic regions" m = mild, v = virulent, vv = very virulent, vv+ = very virulent plus, as explained on page S46, Table 1. To be very clear, Marek is not covid. I am drawing no equivalence. I just point out that Andrew Read's 2021 articlet is built around a weak argument.

jl6 5y ago

What do you think about this article, by the author of the Marek’s disease study, that criticizes extrapolating from the chicken scenario to the covid scenario?: https://theconversation.com/amp/vaccines-could-affect-how-the-coronavirus-evolves-but-thats-no-reason-to-skip-your-shot-165960 https://theconversation.com/amp/vaccines-could-affect-how-th...

angelzen 5y ago
The core argument is that Marek kills in 10 days or less, which is too soon for viral spread to happen. MDV vaccines keep chickens from dying, thus spread of hot variants can occur. Since covid doesn't kill that much, Marek phenomenon can't happen. The obvious issue with the argument is that the hot lethal variants are observed post vaccine availability. Earlier strains were "mild" or "virulent", but not "very virulent plus". "Death was relatively rare". From an 1998 article on Marek, there appear to have been at least 3 jumps in Marek virulence, one in the late '50s pre vaccines (mild => virulent) and two post vaccine availability (virulent => very virulent, very virulent => very virulent plus), see chart on page S50. https://www.tandfonline.com/doi/pdf/10.1080/03079459808419292 https://www.tandfonline.com/doi/pdf/10.1080/0307945980841929... From Andrew Read's own 2015 article: "MDV became increasingly virulent over the second half of the 20th century [19,21–24]. Until the 1950s, strains of MDV circulating on poultry farms caused a mildly paralytic disease, with lesions largely restricted to peripheral nervous tissue. Death was relatively rare. Today, hyperpathogenic strains are present worldwide. These strains induce lymphomas in a wide range of organs and mortality rates of up to 100% in unvaccinated birds." https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002198 https://journals.plos.org/plosbiology/article?id=10.1371/jou... The conclusion of the rebuttal article you linked to is rather terrifying. If there ever was a "the road to [chicken] Hell is paved with good intentions", this is it. "In the history of human and animal vaccines, there have not been many cases of vaccine-driven evolution. But in every one of them, individuals and populations have always been better off when vaccinated. At every point in the 50-year history of vaccination against Marek’s disease, an individual chicken exposed to the virus was healthier if it was vaccinated."
- jl6 5y ago
  > The obvious issue with the argument is that the hot lethal variants are observed post vaccine availability. But is that true? Which hot lethal variants arose post vaccine availability?
  - angelzen 5y ago
    From 1998 https://www.tandfonline.com/doi/pdf/10.1080/03079459808419292 https://www.tandfonline.com/doi/pdf/10.1080/0307945980841929..., page S50, Figure 4: BIVAL vv (late 70s) then RISPENS vv+ (early 90s). The text: "The three major pathotype shifts are: (1) from m MDV to v MDV strains in the late 1950s; (2) from v MDV to vv MDV in the late 1970s; (3) the appearance of the putative vv + pathotype in the early 1990s (Figure 4). Each occurrence has been associated with greater disease losses which have persisted until introduction of the next generation of vaccine. The reason for the shifts remain speculative. Shifts in the 1970s and 1990s may have been in response to certain MD vaccines. Kreager (1996) has suggested vaccines may have only a 10-year useful life before new strains evolve. The shift in the 1950s occurred prior to vaccine use, but may have been related to changes in poultry husbandry, especially the move towards larger houses and the increasing density of poultry operations in certain geographic regions" m = mild, v = virulent, vv = very virulent, vv+ = very virulent plus, as explained on page S46, Table 1. To be very clear, Marek is not covid. I am drawing no equivalence. I just point out that Andrew Read's 2021 articlet is built around a weak argument.