This may be explained by Simpson's Paradox. Something similar happened in Israel, if you look at the raw case numbers for the current wave, it looks like the va

This may be explained by Simpson's Paradox. Something similar happened in Israel, if you look at the raw case numbers for the current wave, it looks like the vaccine only has a ~67% efficiency: https://www.covid-datascience.com/post/israeli-data-how-can-efficacy-vs-severe-disease-be-strong-when-60-of-hospitalized-are-vaccinated https://www.covid-datascience.com/post/israeli-data-how-can-... The UK and Israel both have very high vaccination rates of older people, and lower fully vaccinated rates of younger people. Someone who is 75 most likely has a much weaker immune system than someone who is 25, to the point where someone who is 75 and fully vaccinated may have a much harder time fighting the virus than someone who is 25 and unvaccinated. The data from Israel if broken down by under and over 50s, shows the vaccine efficiency is 92% for under 50s and 85% for over 50s. Israel mainly used Pfizer though, where as the UK mainly AstraZeneca, so there could also be differences there.