The latest UKHSA Vaccine Surveillance report came out yesterday, allowing us to update our estimates of unadjusted vaccine effectiveness. Last week I noted that vaccine effectiveness was stabilising, and this week we can see it rising in the older age groups. Despite this, it is still negative for those aged 30-79, highly so for 40-69 year-olds, and barely positive in the over-80s and 18-29 year-olds.
Part of the reason for the recent rises in the older age groups may be the boosters that have been rolled out since September 20th – you can see a staggered stabilising and then rise across the age groups in the graphs above and below. This means that we are no longer seeing clean data for double-vaccinated versus unvaccinated, as some are triple-vaccinated. The UKHSA report doesn’t include figures for ‘dose three’ and appears to include the triple-jabbed in its ‘received two doses’ category, though oddly does not clarify either way.
The report still claims of course that its data is too biased to be used to estimate vaccine effectiveness, and lists the usual reasons. We await any actual data on the differences between vaccinated and unvaccinated populations, such as testing rates, seroprevalence and prior Covid positives, that would help to account for these biases.
While the raw data shows infection rates often much higher in the double-vaccinated than the unvaccinated, and a number of studies have shown negligible vaccine effectiveness after six months, the official line is that the vaccines remain positively efficacious. Test-negative case-control studies are often used to demonstrate this, which we criticise here. A recent UKHSA study on boosters put the pre-booster effectiveness at 44.1% for AstraZeneca and 62.5% for Pfizer, five months after dose two. Such estimates must be considered upper bounds, given the biases in the case-control design that seem consistently to inflate vaccine effectiveness estimates.
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