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Back to this: It goes without saying that preventing infection prevents transmission. A vaccine that TRULY prevents infection rolled out in a population will put up roadblocks all over the place, breaking chains of transmission easily. We all get that. https://twitter.com/andrew_croxford/status/1351208852356784144?s=20
Itâs the grey area that seems to confuse some people, in that it is absolutely possible to have a vaccine that doesnât prevent infection in ANYONE that can still significantly prevent transmission across a population.
So I've messed around on Powerpoint for you...
So I've messed around on Powerpoint for you...
Youâre at your local Tesco: In walks a SARS-CoV-2-infected guy who refuses to isolate after testing positive. We donât like this person. He is fortunately a rare breed. Purple man infects three people of different vaccination status. Three different stories unfold.
A typical unvaccinated person who contracts SARS-CoV-2 will increase viral load over the course of a few days and remain infectious for a few days, maybe with mild symptoms or without. If he has 15-20 interactions, he may infect a few people along the way. That's how it works.
A person who has a vaccine that genuinely prevents infection (sterilising immunity), as we said is a no-brainer.
Canât get it, canât pass it on.
A slide wasted.
A tweet wasted.
My time wasted.
Your time ⊠wasted.
Canât get it, canât pass it on.
A slide wasted.
A tweet wasted.
My time wasted.
Your time ⊠wasted.
Mr. Green though *is* infected, but the vaccine significantly modifies the course of his infection. There will be many flavors of this guy. There will be some who are closer to sterilizing immunity, there will be genuine non-responders, and everything in between. MANY variables.
But itâs the âaverageâ in the population that makes the difference to transmission. 'On average' these will be less infectious & less symptomatic, but every single person IS potentially infected. They will just have to work harder to pass it on, depending on vaccine efficacy.
My guess? Mr. Greens (and maybe some Mr. Pinks) are the difference in vaccinated arms of these now very famous Kaplan-Meier plots from Pfizer and Moderna (both NEJM papers). These people are the reason for this beautiful flatline that had everyone drooling.
What we DO know, is that the vaccines effectively prevent symptomatic COVID. Those were the trial endpoints, and thatâs how we know that the vaccines are HIGHLY efficacious.
There is still the question of asymptomatics, sure, it wasnât thoroughly tested, I know, I know.
There is still the question of asymptomatics, sure, it wasnât thoroughly tested, I know, I know.
But to get an idea of how efficacious the Pfizer vaccine is, I love the analogy from @FLermyte (who was valiantly attempting to convince a sceptic that these vaccines work), who said...
âTry flipping a coin 170 times, and see if it comes up heads 162 of them. Iâll waitâ.
âTry flipping a coin 170 times, and see if it comes up heads 162 of them. Iâll waitâ.
A picture is emerging that presymptomatics (which are âtechnicallyâ asymptomatic, by the way) and symptomatics can pass the virus around, perhaps to a higher degree than genuine asymptomatics. These are people we know benefit from the vaccines above. https://twitter.com/ArisKatzourakis/status/1351349283237359618?s=20
Today, *it has technically not been shown* that we donât prevent transmission. This is the correct position for leading voices to take. There are attempts to cajole these guys into saying this isn't the case before it's proven (in the USA), which is wrong.
In my humble opinion, I think itâs unlikely that we will turn the world into some kind of asymptomatic transmission conveyor belt. It's safe to say that it is *likely* that a fully vaccinated person will not transmit as well as a naive one after a similar infection event.
Now of course, itâs clear to me that this is a house of cards that could be blown away by the emergence of a variant that manages to modify its spike in such a way that the sequence used to generate the vaccines in January last year. Too much for this thread...
I will go into more detail on this soon but remember, there is still currently no evidence that a fully vaccinated (two doses) individual isn't protected form any-and-all variants of SARS-CoV-2. We should vaccinate in accordance with the trial guidelines, if possible.
We will cross that variant bridge when we come to it. But if you think that Moderna, BioNTech and many others don't already have these variants in the crosshairs, lining up sequences to prepare for this eventuality, I suspect that you are mistaken.
James is to blame for this thread. ;) https://twitter.com/jneill/status/1351487746427256832
