On the JCVI decision, the real question to my mind is who sets the terms of the question being asked for this group, and what precisely they are. It appears the prime criteria are individual hospitalisations and deaths risks, though other factors are considered in part. 1/n
This is conjecture, but it appears that these are calculated over a particular time horizon, and don't factor in the possibility that the overwhelming majority of under 18s will certainly encounter the virus at some point over the coming year on current policy trajectory. 2/n
Of course, these calculations leave out the risk of long term health consequences such as long covid. We are well past the point where the possibility of long term disease needs to be factored into policy. 3/n
More curiously, the remit specifically appears to preclude risk in terms of community transmission, and risk to others more generally. However, and this is an important exception - risk to vulnerable parents is factored in, 4/n
With adolescents living with vulnerable parents being offered the vaccine. So the door is open to community transmission also being included in these kinds of calculations, and its not clear why, and who, explicitly excluded this from the terms of reference. 5/n
More importantly, given that, although the vaccine won't be rolled out to all 12-18s at this stage, it will be rolled out to hundreds of thousands in particular vulnerable, or living with particular vulnerable, individuals. 6/n
So in a sense, JCVI is implicitly in agreement with MHRA that these are incredibly safe vaccines, that they are prepared to allow large numbers of people take. 7/n
They also seem open to the principle of allowing an individual to be vaccinated in order to protect others, while making it clear that they and their families must be fully informed of the decision they would be taking. 8/n
Thus in principle, I don’t think they are closing the door in the long run to vaccination for protecting others. I don't know what the process for revisiting this decision would be but the sooner that occurs, the fewer would have been unnecessarily exposed to covid risk. 9/n
Finally, I hope more details are made available soon and the committee does not allow its position to be defined by the public pronouncements of particular members. 10/n
Postscript-some are arguing this must be down to supply. I think it is more likely to be down to the terms of the questions asked than supply. It is in everyone's interests to be open about the facts if this is really about supply.

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More from @ArisKatzourakis

7 Jul
This is the 'phylodynamic curve', a conceptual model that summarises how viral adaptation rate responds to immune pressure, taken from the following classic paper: 1/n

In theory, we can use this model to make predictions about how the rate of evolution changes in response to changing immune pressure, such as, for example, the rolling out of a vaccine in a population. 2/n
One might imagine, for example, that as the vaccine is rolled out, we move from low adaptation at low levels (area 2 in the figure), to intermediate levels (area 3), and eventually over the hump to low levels again (area 4), tending to low values eventually. 3/n
Read 8 tweets
22 Jun
I imagine this thread will be shared heavily in the context of the lab leaks discussions, which it actually says almost nothing about. Very interesting data & analysis.
Also, Google Cloud as a viral fossil-bearing stratum...#paleovirology

Read 4 tweets
11 Feb
[MEDIUM THREAD] On the topic of covid becoming an endemic virus. You hear this a lot; sometimes in response to critiques against strategies of elimination, sometimes just as a statement in its on right. Statements such as “Covid will inevitally become endemic.” 1/n
The problem is, most of the time, I am not convinced people quite understand what endemic means. An endemic virus is a virus where infection levels are maintained at a baseline level without external inputs. Chickenpox is endemic; HIV is not, as it is still spreading. 2/n
Achieving an endemic steady state requires a very particular set of conditions, namely that R(0) X the proportion of susceptible individuals in the population, is equal to 1. This would lead to a steady state, a fixed number of infections, which neither grow nor fall. 3/n
Read 15 tweets

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