Archives For Covid 19

ATAGI provided an estimate of the risk associated with TTS events (bad post vaccination events). This was at the time based on the evidence that was available. The problem with this is that we run into de Moivre’s `Law of Large Numbers’. Which in essence says we can expect small samples to have much greater variability than larger sample sizes. As a result when tracking vaccine side effects you can expect the estimated rate of occurrence to be all over the shop initially because one incident against a very low number of vaccinations (our sample) can skew the incident rate a lot.

To give you a feel for this effect our friend de Moivre found that the size of a typical discrepancy (variance) goes up proportional to the square root of the number of samples. As we divide that number by the total number of samples to get our proportional rate the proportional discrepancy is going to increase as our sample gets smaller. It’s a bit like throwing a small rock into a small pool (big splash proportionally) and then retreiving it and tossing it into a big lake (small small splash proportionally).

So what ATAGI did wrong with their initial estimate of TTS was not considering that for a very rare event like TTS the population needed to dial back the variance associated with a proportionally small size sample was going to big, and the needed to account for it. But they didn’t. Instead the just threw up the raw frequencies in the risk assessment. Of course the world has moved on and it turns out that the initial TTS estimates totally over estimated the rate of TTS. Well I guess a 17th century mathematician still has a few things to teach AGATI.

So in a previous post I outlined why the risk comparison that ATAGI purported to perform was fatally flawed. But unfortunately it’s worse than that.

ATAGI’s risk comparison is based on a side by side comparison of TTS occurrence rates agains Covid 19 deaths for a specific age cohort. But this is only valid if all TTS result in death. On the face of it that didn’t seem right, so I went and pulled the prior ATAGI advice and as it turns out, based on their data, the risk of death is 3% if you get a clot. So the actual risk of death due to TTS risk is 0.081 per 100,000 in the age group 50-59. Compared to the estimated risk of Covid 19 death for the age group 50-59 in a moderate outbreak of 0.1 per 100,000. Close enough to say the risk is equivalent.

Putting is simply and bluntly ATAGI managed to overestimate the risk of TTS by two orders of magnitude. That overestimate runs all the way through the rest of their risk estimates heavily skewing it against Astra Zeneca. Why did such a basic error occur? Well it’s pretty much an open secret there’s been an ongoing internal factional fights within ATAGI regarding Pfizer versus Astra Zeneca and I’d surmise that when whoever put this risk assessment together got the number they expected (wanted to see) and didn’t bother to check it.

If ATAGI had just checked the damn numbers they wouldn’t have made the stupid error that they did, they wouldn’t then have issued the advice that sent the Commonwealth Government into a flat-spin and led to the trashing of Astra Zeneca. Astra Zeneca being the only vaccine we had much of at that time. Slow hand clap for ATAGI.

In an alternate universe of course someone did pick up the error, the advise remained unchanged, that limousine driver in Sydney did get his Astra Zeneca jab and the Delta outbreak in Sydney never took off. I’d really like to live in that universe wouldn’t you?