I think this final graph is a bit confused here, unless ‘the original strain’ here means Delta. Delta had about a 120% advantage over ‘the original strain’ or 70% over Alpha. I’m going to take this to mean 500% as compared to that 120%, so 600% of original versus 220% of original, or about a 170% additional increase. Which is… better, but still quite a lot.
I’m pretty sure the graph is trying to say 500% over delta. If you run the numbers on a very similar graph, you get that the new disease is slightly above 5.5 times as infectious as delta, which you could round to a 500% increase. (Assuming identical generation length. Also, I haven’t looked into sources for the numbers.)
South Africa’s vaccination rate is sufficiently low, and this rate of spread so high, that it wouldn’t much matter if there was vaccine escape properties, although it would presumably matter if there was escape from natural immunity.
I don’t know why you expect a large difference there. I’d guess that roughly equal numbers of people in south africa has been vaccinated as has natural immunity.
Or, okay, I can see two reasons to expect natural immunity to be a bigger deal:
natural immunity is more common in the most exposed part of the population.
there’s more uncertainty about the amount of natural immunity in south africa, and if south africa has very sizeable natural immunity and there’s substantial immunity erosion, that would be a pretty good explainer for why omicron would be spreading so much faster than delta. So there’s some bayesian update towards south africa having sizeable natural immunity.
5x Delta transmissibility seems insane. I… Don’t have gears level models which prohibit such a thing, but wouldn’t that give it a reproduction rate between 25 and 45?! Even chickenpox is only 12.
A factor 1.5-3 of that could be immune erosion, in which case the R0 would be more like 10-20. And more importantly, I don’t know anything that contradicts Zvi’s intuition that this little data shouldn’t push us far away from our priors.
I’m pretty sure the graph is trying to say 500% over delta. If you run the numbers on a very similar graph, you get that the new disease is slightly above 5.5 times as infectious as delta, which you could round to a 500% increase. (Assuming identical generation length. Also, I haven’t looked into sources for the numbers.)
I don’t know why you expect a large difference there. I’d guess that roughly equal numbers of people in south africa has been vaccinated as has natural immunity.
Or, okay, I can see two reasons to expect natural immunity to be a bigger deal:
natural immunity is more common in the most exposed part of the population.
there’s more uncertainty about the amount of natural immunity in south africa, and if south africa has very sizeable natural immunity and there’s substantial immunity erosion, that would be a pretty good explainer for why omicron would be spreading so much faster than delta. So there’s some bayesian update towards south africa having sizeable natural immunity.
Don’t know where this nets out.
5x Delta transmissibility seems insane. I… Don’t have gears level models which prohibit such a thing, but wouldn’t that give it a reproduction rate between 25 and 45?! Even chickenpox is only 12.
A factor 1.5-3 of that could be immune erosion, in which case the R0 would be more like 10-20. And more importantly, I don’t know anything that contradicts Zvi’s intuition that this little data shouldn’t push us far away from our priors.