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I vaguely recall people talking about human/malaria co-evolution. And I was of the impression that the malaria parasite was supposed to be good at evading our i

by abeppu 6y ago

I vaguely recall people talking about human/malaria co-evolution. And I was of the impression that the malaria parasite was supposed to be good at evading our immune system, and that was part of why vaccines had limited efficacy. If anyone here is educated in this area ... would it be reasonable to expect that the 77% efficacy would decline if such a vaccine were put into widespread use? Like, I know we observe a pattern where antibiotics become less effective if they are deployed widely. Or are protists slower / less able to evolve in response to this kind of intervention?

asdfasgasdgasdg 6y ago
It depends on a lot of things. First is how easy it is to evolve a way around a particular defense. For example, it will be easier to achieve an vaccine escape when only one gene is required to mutate compared to ten thousand. If you have a vaccine that disrupts something fundamental about a pathogen's lifecycle, it's better than one that targets something superficial. Another question is what fraction of the population is exposed to the selective pressure, and to what extent the selective pressure confers a benefit or cost to all other members of the population. If responding to the pressure makes the population more fit in other hosts, then we should expect it to become widespread eventually. On the other hand, if it causes the disease to become less efficient in other hosts, you would not expect the mutation to become widespread. For example, imagine if there were a monster that lived in a small part of Alaska that tended to eat humans with small fingers, we would probably just not go to that part of Alaska. On the other hand, if such monsters were present throughout the world, you'd probably see humans with longer fingers over the generations. Does that make any sense? It's a strained metaphor but I hope it gets the point across. Another thing that can happen is speciation, but we'll leave that for another day.
bullfightonmars 6y ago
There is a key sentence of this article that speaks to this: > This new vaccine (R21) uses a circumsporozoite protein (CSP) antigen – that’s a highly conserved protein of the parasite, involved in several functions as the parasite makes the move from mosquito to human and into different human tissues such as the salivary glands. Circumsporozoite protein is a highly conserved protein meaning that it is a genetic sequence that is very unlikely to change regardless of adaptive/evolutionary pressure.
- abeppu 6y ago
  I see. So the 23% does not suggest that, e.g. there's some minority of parasites that are "immune" already.
  - jjk166 6y ago
    Not necessarily - vaccine effectiveness also relies on the person's immune system actually developing the needed antibodies. Some fraction of people simply won't. This is also why vaccine effectiveness goes up with multiple doses - sometimes the first one doesn't take but the second one does.

by abeppu 6y ago

asdfasgasdgasdg 6y ago

It depends on a lot of things. First is how easy it is to evolve a way around a particular defense. For example, it will be easier to achieve an vaccine escape when only one gene is required to mutate compared to ten thousand. If you have a vaccine that disrupts something fundamental about a pathogen's lifecycle, it's better than one that targets something superficial. Another question is what fraction of the population is exposed to the selective pressure, and to what extent the selective pressure confers a benefit or cost to all other members of the population. If responding to the pressure makes the population more fit in other hosts, then we should expect it to become widespread eventually. On the other hand, if it causes the disease to become less efficient in other hosts, you would not expect the mutation to become widespread. For example, imagine if there were a monster that lived in a small part of Alaska that tended to eat humans with small fingers, we would probably just not go to that part of Alaska. On the other hand, if such monsters were present throughout the world, you'd probably see humans with longer fingers over the generations. Does that make any sense? It's a strained metaphor but I hope it gets the point across. Another thing that can happen is speciation, but we'll leave that for another day.

bullfightonmars 6y ago

There is a key sentence of this article that speaks to this: > This new vaccine (R21) uses a circumsporozoite protein (CSP) antigen – that’s a highly conserved protein of the parasite, involved in several functions as the parasite makes the move from mosquito to human and into different human tissues such as the salivary glands. Circumsporozoite protein is a highly conserved protein meaning that it is a genetic sequence that is very unlikely to change regardless of adaptive/evolutionary pressure.

abeppu 6y ago
I see. So the 23% does not suggest that, e.g. there's some minority of parasites that are "immune" already.
- jjk166 6y ago
  Not necessarily - vaccine effectiveness also relies on the person's immune system actually developing the needed antibodies. Some fraction of people simply won't. This is also why vaccine effectiveness goes up with multiple doses - sometimes the first one doesn't take but the second one does.