From reading the report I think this is addressed p36 that might be because the vaccinated and unvaccinated population are different in other ways :

> 1Comparing case rates among vaccinated and unvaccinated populations should not be used to estimate vaccine effectiveness against COVID-19 infection. Vaccine effectiveness has been formally estimated from a number of different sources and is summarised on pages 5 to 11 in this report. The case rates in the vaccinated and unvaccinated populations are unadjusted crude rates that do not take into account underlying statistical biases in the data and there are likely to be systematic differences between these 2 population groups. For example: • people who are fully vaccinated may be more health conscious and therefore more likely to get tested for COVID-19 and so more likely to be identified as a case (based on the data provided by the NHS Test and Trace) • many of those who were at the head of the queue for vaccination are those at higher risk from COVID-19 due to their age, their occupation, their family circumstances or because of underlying health issues • people who are fully vaccinated and people who are unvaccinated may behave differently, particularly with regard to social interactions and therefore may have differing levels of exposure to COVID-19 • people who have never been vaccinated are more likely to have caught COVID-19 in the weeks or months before the period of the cases covered in the report. This gives them some natural immunity to the virus for a few months which may have contributed to a lower case rate in the past few weeks

But all these factors would impact equally covid cases and covid deaths (since the UK definition of a covid death is a covid case who died), so you would still expect a reduction of the % vaccinated from one to the other. And by September all the vaccination curves plateau-ed, so it's unlikely to be a timing issue.

> the UK definition of a covid death is a covid case who died

This is what a bunch of us have been complaining about all along. Not everyone with COVID who dies actually died because of COVID.

I thought that but 1) the economist numbers seem to confirm the covid deaths numbers at least for the UK, and 2) you get roughly the same numbers of daily covid deaths [1] by "tested positive in last 28 days" vs "covid on death certificate". So while it is an explanation that would match the data, I don't know if that's true.

[1] https://coronavirus.data.gov.uk/details/deaths

The footnote on p33 and 34 suggests an explanation, namely that vaccination rates among the elderly (where most of the deaths are) are particularly high. E.g. if the unvaccinated elderly are outnumbered by the vaccinated 1 to 20, then if the vaccines have an 80% effectiveness against mortality you'd still expect deaths among the unvaccinated to be outnumbered 1 to 4.

But that would affect equally both covid cases and covid deaths. But if you focus on the elderly, for say >70yo, vaxed are 87% of covid cases, and 84% of covid deaths. If the vaccine was 90% efficient, you would expect the vaxed death to be 40%, not 84% (84% implies a 15% vaccine efficiency).

> If the vaccine was 90% efficient, you would expect the vaxed death to be 40%, not 84% (84% implies a 15% vaccine efficiency).

I'm not too sure how you arrived at your figures, but here's my back of the envelope calculation for the percentage of either expected deaths or expected cases coming from the vaccinated part of an age group:

  V * (1 - E) / ((1 - V) + (V * (1 - E))

where V is the percentage of the age group that's vaccinated (~95% for >70yo) and E is the effectiveness against either death or symptomatic disease (which isn't exactly the same as a case, I know), i.e. only (1 - E) of the vaccinated population will face death or symptomatic disease.

Playing around with the effectiveness values, 87% of cases and 84% of deaths from the vaccinated in the >70yo group doesn't look impossible.

If you have a population of 100 positive cases, 87 vaxed, 13 unvaxed. Let's assume the unvaxed death rate is 100% (it doesn't mater).

If the vaccine is 90% efficient, then 10% of the 87 vaxed will die, 100% of the 13 unvaxed will die, therefore the % of vaxed in the deaths will be (we are using the same formula) 10% * 87 / (10% * 87 + 13) = 40%

If the vaccine is 15% efficient, then 85% of the 87 will die, and the % of vaxed in the deaths will be 85% * 87 / (85% * 87 + 13) = 85%

You're using "efficient" to mean effectiveness against death given infection, but the vaccines aren't close to 90% effective against that. [1] says they're 54% effective against death given infection, which actually predicts 78% of deaths being in the vaccinated if you plug it in to the formula.

[1] https://assets.publishing.service.gov.uk/government/uploads/...