Take care with claims about unvaccinated case rates

一世TV’s political editor, Robert Peston, wrote a Twitter thread with the headline: “Infections higher among double vaxxed for those [老龄化] 40 到 79 than for non-vaxxed.” ITV changed that headline, but Peston was surprised that these figures “occasioned so little debate”. So let’s debate them.

一种 Public Health England report 上 9 September showed that over the previous four weeks there had been, 例如, 多于 97,000 cases among people aged between 40 和 49. The huge majority (多于 82,000) had been vaccinated. This is expected when vaccine coverage is high and protection not perfect: most car occupants who die in road incidents are wearing seatbelts.

The surprise came from the reported case rate per 100,000 population being higher for fully vaccinated people (1,116) 老龄化 40 到 49 than for unvaccinated (880), which appears to question the effectiveness of the vaccines. But the problem is that we don’t know how many people have not been vaccinated, because we don’t know how many people live in England, thus demonstrating the need for the recent census.

PHE uses National Immunisation Management System (Nims) estimates of 8.1 million adults aged 40 到 49 in England. These numbers depend on GP records and tend to overcount. The Office for National Statistics (我们) also produces population estimates, based on the 2011 census, migration and death registrations and estimates 7.1 million adults in that age group, a million fewer than Nims.

Up to 5 九月, NHS England reported 6.4 million people in that age group had received a Covid-19 vaccine dose. So the ONS population estimate leaves about 700,000 unvaccinated people aged 40 到 49, while using Nims means 1.7 million. This is a massive difference.

ONS figures will not be perfect, but suggest about 2,000 confirmed cases per 100,000 unvaccinated people aged 40 到 49, twice the rate as in the vaccinated group, and roughly what we might expect. 相似地, ONS estimates give lower case rates in fully vaccinated people than unvaccinated in all ages below 80. There may also be other differences between vaccinated and unvaccinated groups, including the propensity to get tested.

It is unfortunate Robert Peston’s tweets have been misinterpreted by those sceptical of vaccines.