>>I was not too worried on side effects of AZ, but felt that short term benefit of getting AZ vaccination in May vs. mRNA as possible choice starting end of July reasonable due to much higher efficacy (.90 does not sound that bad compared to .96, but when calculated as 1-efficacy, 10% vs 4% of catching Corona [not Covid19, but similar differences expected there as well] is something to consider).

In the UK, NHS Briefing 19 found that for Delta C19 infections in the Feb-July 2021 period, 28,773 were fully vaccinated, 54,091 had received first dose, and 121,402 were unvaccinated. Of the unvaccinated, only 2,337 were in the over 50 group which is likely to be a prioritization artifact. Of deaths (using their unusual "within 28 days of positive test" definition) 224 were fully vaccinated, 65 partly vaccinated and 165 unvaccinated which yields an 0.77% death rate for fully vaccinated versus 0.13% for unvaccinated which is similar to the annual flu mortality.

As always the devil is in the detail: break the figures into >50 age bracket and suddenly the case counts are lower for unvaccinated while death rate is significantly higher: 220 deaths in 13,427 vaccinated cases, versus 110 deaths in 2,337 unvaccinated cases.

These >50 figures appear to support your logic, though we'd want to see overall vaccinated vs unvaccinated denominators to confirm whether the vaccine protects from infection or simply reduces mortality/severity in the >50 group.

Latest Briefing 20 this week: data presentation changes yet again, but: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1009243/Technical_Briefing_20.pdf ... See 1.7 Vaccination: no significant difference in Ct load vaccinated vs unvaccinated, meaning no difference in infectiousness/risk to others whether vaccinated or not. Hence updated advice for vaccinated people to wear masks: these vaccinates won't establish herd immunity and the promise that vaccination would set you free was premature, since once infected you're Typhoid Mary even if you got your shots.

There is good news: check out all the named variants and upcoming variants awaiting labels in Briefing 20. Most are short lived; as of today, 99% of C19 infections are sequenced as delta so once that starts to diminish, this one could follow the curious pandemic pattern that the bug seems to "lose heart" and fade away, as Ebola and various earlier swine flus did.