The latest Technical Briefing on the Variants of Concern, number 23, has been published by Public Health England (PHE), so we can update our (unadjusted) estimates of vaccine effectiveness against the Delta variant using the data it includes from sequenced Delta samples from positive PCR test results in England.
As before, we subtract the figures in the latest briefing, now no. 23, from those in briefing 17 to give the figures for the period June 22nd to September 12th. This gives us a picture for the whole Delta surge, which allows for the fact that most of the early reported infections were in the unvaccinated and most of the later reported infections were in the vaccinated (see below). PHE has recently also published the most recent month’s data for all reported infections (not just sequenced Delta ones), which shows lower vaccine efficacy in the most recent four weeks (a new report released on Friday shows this has dropped even further in the most recent week). However, given the apparently delayed infections in the vaccinated, it seems most accurate to look at the figures for the whole surge, not just the last month, when estimating vaccine efficacy against Delta.
We also use figures for proportions of the population vaccinated by age derived from the PHE Covid surveillance reports.
Starting with the over-50s, for the period June 22nd to September 12th, PHE reports 68,445 Delta infections in the double vaccinated and 7,575 in the unvaccinated. PHE figures show that in this period the proportion of the over-50s double vaccinated increased from 87% to 89%, giving a mean of 88%, and the proportion unvaccinated was stable at 9%. Calculating the vaccine effectiveness against Delta infection in the over-50s (1-(68,445/88%)/(7,575/9%)) gives a figure of just 7.6%. This is down from 15% two weeks ago and 24% two weeks before that. This continues to be very different to the estimate in the recent Oxford University study using ONS survey data, a study which I criticised for numerous inconsistent and implausible findings.
Read more: New PHE Data Shows Vaccine Effectiveness Against Delta Down to Just 7.6% in the Over-50s, 24% in the Under-50s, as the [Fake] Vaccinated Continue to Experience Higher Infection Rate [consequences for having the fake vaccine]