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The Office for National Statistics (ONS) have released the latest data from their COVID-19 Infection Survey.
Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:
“The latest ONS bulletin on antibodies in their testing of the UK population essentially covers February (actually the 28 day period 4 February-3 March). The ONS estimate of the number of people in the community populations of the four UK countries who would test positive for antibodies, if tested during that time, increased hugely compared to the previous 28 days (which were mostly in January). It more than doubled in Wales and in Northern Ireland, almost doubled in Scotland (88% increase), and though the percentage rise in England was a bit smaller (77%), that’s probably because there had been a bigger rise in England in the previous bulletin. As a result, in three of the UK countries (England, Wales, and Northern Ireland) about 1 in 3 people would have tested positive for antibodies during February – and with the continuing success of the vaccination programme, the numbers are likely to be higher than that already. In Scotland, the proportion testing positive is a bit lower – about 1 in 4. I don’t believe this has anything to do with differences in vaccination progress between Scotland and the other countries. It’s mostly or entirely because the percentage of people in Scotland who were infected with the virus during the peak in December and January was lower in Scotland than in the other three countries. The ONS antibody data come from antibody tests on a reasonably representative sample of the community population aged 16 and over, so aren’t affected by people choosing to ask for antibody tests for some reason. The tests look for antibodies to SARS-Cov-2, the virus that causes Covid-19, but they cannot distinguish between antibodies that arise because the person was infected with the virus, and antibodies that arise because the person was vaccinated.
“There’s good evidence from the data that a great deal of the increase in people testing positive for antibodies is due to vaccination. That shows up because the percentage of people with antibodies is highest in the oldest age groups. In England, ONS estimate that three quarters of people aged 80 and over would test positive for antibodies. The proportions in the next age groups down are a bit smaller (69% for ages 75-79, 55% for ages 70-74), but are still considerably above the proportions for younger people, which are below a third. This makes sense in terms of what we know about the vaccination programme. It takes a couple of weeks for antibodies to show up clearly in someone’s blood after they are vaccinated, so people testing positive for antibodies in these survey results because of vaccination would have to have been vaccinated by about mid-February at latest. Up to that date it was only those aged 70 and over who had received vaccination on a mass scale, and people at the lower end of that age group would have been vaccinated towards the end of that period (and some of them would not have been vaccinated yet). Younger people would have been vaccinated only if they were health or care workers or had certain health conditions, so a much smaller proportion of the younger age groups would have been covered and vaccines would have had a much smaller effect on antibody positivity.
“In broad terms, the same kind of pattern with age shows up in the other three UK countries, though the survey estimates there have considerably wider margins of error than in England, because fewer people are tested in the survey because the populations are smaller. The pattern that older people are more likely to be antibody positive is still very clear. The rate of antibody positivity in people aged under 70 is lower in Scotland compared to the other three countries – under a fifth of the under 70s were positive for antibodies in Scotland, compared to between an quarter and a third elsewhere. Since most of those younger people in all four countries wouldn’t have been vaccinated in time to show up in these numbers, that must be because fewer of the younger Scots were naturally infected with the virus – and we know that’s the position from ONS data on infection levels during the latest peak and from counts of confirmed new cases on the dashboard at coronavirus.data.gov.uk. As vaccinations are rolled out to younger age groups, the differences between countries will smooth out. The same goes for differences between the English regions, where antibody positivity rates across all ages range from 39% in the North West to 29% in the South West, and broadly match what’s known about previous levels of infection in different regions.
“Since this is a survey of the community population, it doesn’t include people living in communal establishments such as care homes. Because a large proportion of care home residents are over 80, this means that the percentage of all those aged 80+ who are antibody positive will probably differ from the figures here, and it will probably differ in different ways in the different UK countries because of differences in care home coverage. But we can be confident that the antibody positivity rate in the oldest people across the UK is now very high.”
All our previous output on this subject can be seen at this weblink:
www.sciencemediacentre.org/tag/covid-19
Declared interests
Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee. I am also a member of the Public Data Advisory Group, which provides expert advice to the Cabinet Office on aspects of public understanding of data during the pandemic. My quote above is in my capacity as an independent professional statistician.”