There is a lot of confusion here in vaccinated Tel Aviv, now that around 50% of people infected with COVID appear to be full vaccinated. Newspapers are heavily quoting the “64% i.s.o 90% for the Delta variant” which does not seem to be based on the correct calculation of vaccine effectiveness.
I used an explanation by Dvir Aran to make a slide that explains how it is expected that 50% of infected people are fully vaccinated, even with a 90% vaccine effectiveness.
The logic is as follows:
Take 100 people who are seriously exposed to the virus
Assume a 90% vaccination rate (the case for the at-risk population in Israel at the moment):
A small group is exposed: 10 people
A big group is protected 90 people
Assume a 90% vaccine effectiveness:
10 out of 10 unvaccinated people will get infected
8 out of the 90 vaccinated people will get infected
Of the total of 18 infected people, 8 will be fully vaccinated, so around 50/50
Of those 18, the majority of cases with symptoms and serious complications will be unvaccinated of course.
I have added this slide to the SlideMagic library, search for “COVID” and it will pop up, or download it here. Pro subscribers can convert this chart to PowerPoint, if you have to. (Students, you can claim a free membership!).