Here's the breakdown (excluding those with just one shot) since their Delta outbreak began. Iceland population is 364,000. Fully vaccinated population is 255,000. Unvaccinated population is therefore 109,000 (20,000 or so of which have one shot, but for simplicity's sake, let's just say all 109,000 are unvaccinated).
1,386 / 255,000 * 100,000 = 543.
619 / 109,000 * 100,000 = 568.
Basically the same rate...
I thought you preferred tighter time interval windows since so many variables change over a longer period of observation?
Anyway, as you can see by the chart, the trendline is heading towards vaccinated people being less of the share of infected.
What's going on in Iceland, Israel, the UK, and any other place with high levels of vaccination rates is the base rate bias.
Learn to watch out for cognitive biases when thinking about vaccines.
www.psychologytoday.com
Delta has arrived in Israel, and with its arrival, cases are increasing (albeit relatively small).
yourlocalepidemiologist.substack.com
Base rate bias
This is likely an example of
base rate bias in epidemiology (it’s called base rate fallacy in other fields). Professor Levy said that “half of infected people were vaccinated”. This language is important because it’s very different than “half of vaccinated people were infected”. And this misunderstanding happens all. the. time.
The more vaccinated a population, the more we’ll hear of the vaccinated getting infected. For example, say there’s a community that’s 100% vaccinated. If there’s transmission, we know breakthrough cases
will happen. So, by definition, 100% of outbreak cases will be among the vaccinated. It will just be 100% out of a smaller number.
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Cue Israel. They are one of the
global leaders in vaccinations;
85% of Israeli adults are vaccinated. So, say we have the following scenario:
- 100 adult community
- 4 COVID19 cases
- 50% of cases were among the vaccinated
It would look something like this:
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With an infection rate among the vaccinated of 2% and infection rate of 13% among the unvaccinated, this would give us an efficacy rate of 85%. This is pretty darn close to the clinical trial efficacy rate, meaning the Pfizer vaccine is still working against Delta.
Unfortunately, this gets more complicated. We know the original Israeli outbreaks were in two schools. Because the vast majority of kids in Israel are not vaccinated (only 2-4% because they were just approved), imbalance is introduced. But, I ran the numbers and as long as at least 90% of the adults in the original outbreak were vaccinated, we know the vaccine is still working against Delta. 91% isn’t a farfetched number as teachers (at least in the US) are vaccinated at a much higher rate than the general public.
Why increasing Covid infections amongst the vaccinated isn’t necessarily bad news.
www.bbc.co.uk
Looks like they've got some good data by age group, so maybe I'll try to break it down even further later unless you want to do that first.
Someone else already did. He eliminated the 16 and under group from consideration since they aren't even eligible for the vaccines and did an analysis with adults only.
Summary: In a population where a vast majority is vaccinated, looking at the
number of Covid cases will provide a potentially misleading view of vaccine effectiveness against infections. The
case rate provides a much more meaningful comparison.
The reason is that the share of the population that is vaccinated in Iceland is exceptionally high. In fact one of the
highest in the world:
This causes a "denominator problem". Even at a fairly low rate of cases among the vaccinated group, the absolute number of cases is likely to be as high or higher than that among those not vaccinated. And the bigger the share of those vaccinated, the more it will skew a comparison of the raw case numbers.
There is a clear and significant difference in the case rate among those that are vaccinated and those that are not. Furthermore the trend seems to be diverging between the groups with the rate among those not vaccinated still going up while leveling off or falling slightly among the vaccinated.