Its confusing, my interpretation of these figures is;
If you are aged 80+ then the chance of hospitalization has fallen to 20% of what it was ie 80% reduction. and deaths have fallen by 85% from what they were. Given the the Case fatality rate (CFR) for 80+ bracket was 56% last summer ( I think its much lower now due to better treatment) then I suppose the CFM for 80+ years olds is now about 7.5% (15% of 50%) and for the average male its dropped from 4% to 0.6%. its very low people below the age of 40 in any case. These figures seem conservative as I'm read elsewhere that fatalities are virtually zero after 4 weeks, as recent deaths seem to be in people who caught covid within two weeks of the vaccine. There have been studies of care homes that are encouraging. I'll see if I can find them - just need to get a bit more gardening done tonight or I'll get shouted at ....
Chris - I've done a bit of google this lunchtime, here are two articles that we can probably trust. Looking at the raw data, its clearn that we should be multiplying the benefits of vaccination in reducing infection and then in reducing hospitalization or deaths as both the studies measure improvements in death rate and hospitalisation on those already infected. So in summary. The vaccines reduce the chance of hospitalision for the over 70s to 2.5% vs those not vaccinated and deaths in the 80+ aged group to 0.7% compared to those not vaccinated.
The first is government blog from 21 February - note its quite old, but it supports the Johnson/Whitty numbers.
COVID-19: analysing first vaccine effectiveness in the UK - Public health matters
But intriguingly ends by quoting a public heath Scotland report showing vaccine effectiveness of 85% for Pfizer and 94% for AZ and that recent PHE data will be published to support the Scottish numbers - not seen it published yet.
The second article is a published report from PHE - I think this is where BJ and Whitty get there numbers:
https://assets.publishing.service.g...e/971017/SP_PH__VE_report_20210317_CC_JLB.pdf this is quite comprehensive, probably using data gathered in January and February in care homes and the community so probably from data gathered 6 weeks ago. Both of these studies will be showing vaccination effectiveness against a mix of variants that were circulating at the time, the dominant one being the Kent variant estimated to be 96% of cases by the beginning of February.
If we look at the PHE study and do some maths.
First set of table are effectiveness of vaccine against infection as indicated by PCR tests average of 72% in 70+ years olds ie 28% got covid (70+ olds were the ones vaccinated at that time). Its safe to assume younger people will show a greater resistance to covid than this.
Of those that got covid 8.5% were hospitalised, so of those vaccinated 28%* 8.5% that is 2.5% went to hospital with COVID compared to 15% of unvaccinated group.
In numerical terms its was 9000 cases of unvaccinated people led to 1361 hospitalisations, wheres for the vaccinated only 2000 got covid and 172 were hospitalised. Again its safe to assume the younger age groups would be more protected.
Note the different numbers used in headlines, this is where statistics is hard for the lay person to comprehend from newspaper headlines. The vaccine reduced hospitalisations of those infected in this age group by about 40% BUT that is the IMPORTANT BUT, they were already less likely to be infected so you have to multiply the two benefits together to get the overall benefit, ie only about 2% of vaccinated group (9000 unvaccinated got covid cf 172 vaccinated ended up in hospital) vs to 15%, 2% vs 15% is an improvement of 8 fold. In absolute numbers: 172 went to hospital of those vaccinated but 1361 unvaccinated went to hospital. The statisticians don't do what I have just done as you cant be sure that 9000 people got exposed to Covid in both gourp of people - the vaccined vs the unvaccinated . But the overall effect is much more pronounced that the Johnson numbers indicated.
Death rates (CFR):
Here the data is for the over 80s (not comparing like with like as it was the over 70s in the previous data set, as it was the over 80s who had the vaccine and survived or died within 28 days whereas the over 70s hasn't had the vaccine for 28 days during the period of the study so this is very much a worse case scenario as younger aged groups are less likely to die,
Here the overall conclusion is it reduce deaths by 54% of those who caught covid. 13% died unvaccinated vs 6.6% vaccinated an improvement of 54% BUT again that is on a number that is already reduced by the vaccine so the true ratio is 8625 unvaccinated got covid of whom 1115 died whereas only 914 vaccinated got covid of whom 60 died. to my mind that is a 60 out of 8625 (who were exposed to coved) who died or 0.7% - again not statistically a valid thing to do but it kind of give the real world numbers. If you bear this in mind for younger aged groups this is very reassuring as the data is almost certainly for the Kent variant of covid.
Incidentally the Scottish PH number of 94% mentioned in the first article - the blog - may be explained by the data in the second article.
In this study 1115 unvaccinated died compared with 60 vaccinated that is only 6% (5.3% precisely) of vaccinated died ie the vaccine reduced deaths by 94%