there is no way of proving that vaccines worked at all
Eritrea still doesnt use the covid vaccine, they have never used it, they have had 103 deaths due to covid out of a population of 3.6 million
England has 56 million with 202,000
Thats way more per capita and England had one of the earliest vaccine roll outs
there is a way to prove it as far as one can prove it. The in vitro studies and immunology tells us it would work, its jut how bodies work.
Using a isolated super undeveloped nation with a low density of people, that would have horrible reporting, testing etc to the UK is apples to oranges of course.
The US had more per capita than Englad and had ample vaccine. The countries with the lowest per capita were the undevloped ones, I wonder why. A conspiracy theorist would say its because covid wasn't bad and vaccines caused the death or the rational person could point out the climate (huge impact on transmission), poor reporting and testing that likely went on.
To even make your point sensible and not an outlier for example - maybe these folks were innately immune etc we would need to compare all the other countries to reduce the risk of noise