Nearly one in five adults in England – the equivalent of 8.3million people – had coronavirus antibodies at the beginning of February, a major surveillance study revealed today.
The Office for National Statistics (ONS) took blood samples from 30,000 over-16s across the country and found 18.5 per cent tested positive for antibodies, up from 10 per cent in December and 15 per cent in January.
Antibodies are proteins made by the immune system in response to infection or vaccination and their presence generally means someone has either partial or total immunity against catching a disease again.
The number of people testing positive for them has started to increase at a much faster rate in the past two months, which officials say is down to a mixture of Britain’s successful jab roll out and high transmission from the second wave.
The virus-fighting proteins were most common among those aged 80 and over (41 per cent), which the ONS said was ‘most likely due to the high vaccination rate in this group’. Figures show more than nine in 10 over-80s have now had their first dose.
Britain’s Covid immunisation drive prioritised people in the age group, as well as care homes residents and patients who have other life-threatening illnesses, because they are the most vulnerable to dying from the virus.
Across the rest of the UK, the ONS estimates one in seven people have Covid antibodies in Wales, the same number in Northern Ireland and one in nine in Scotland. But the figures will be an under-estimate because millions more people have been vaccinated since the final day of the survey on February 1.
It also takes three weeks for immunity to kick in after getting the jab, which means a large number of the elderly people who were included in the survey would not have had antibodies when they gave their sample.
Antibodies are also known to fade over time, which means people who may have caught the virus during the first wave no longer have measurable levels of the proteins.
The ONS’s survey, which collects regular blood samples from a group of people intended to represent England’s population, showed there was significant variation in antibody positivity between regions.
In London, an estimated one in four had antibodies against the disease by February 1, which was the highest rate across the country, compared to just 11 per cent in the South West.
The North West saw the second highest antibody rate (22 per cent), followed by the West Midlands (21 per cent) and Yorkshire and the Humber (20 per cent). It means four out of nine regions had levels higher than the England average.
While antibodies were most common in over-80s in England, this was not the case in any of the other home nations. In Wales, for example, the highest percentage of people testing positive was those aged 16 to 24 at 33 per cent, with just 13 per cent of over-80s having antibodies.
In Northern Ireland, people aged 25 to 34 were most likely to have the virus-fighting proteins in their blood (22 per cent) and in Scotland it was those aged 16 to 24 years at 15.5 per cent.
The ONS said that small sample sizes in the devolved administrations meant there were bigger confidence intervals – for comparison Wales looked at just 53 over-80s and Scotland tested 107, compared to 1,300 in England.
The survey also only went up to February 1. At that point only 9million people around the UK had been vaccinated, compared to 15.3million as of yesterday.
Because it takes three weeks for antibody levels to build up after a vaccine, an even greater number of people would have been missed by the survey.
Reacting to the findings, Professor Kevin McConway, a statistician at the Open University, said: ‘In previous ONS releases of data from their infection survey about antibodies, we could interpret them as telling us about the numbers of people who had previously been infected by the virus, because for the great majority of people that was really the only way that antibodies could have arisen in their blood.
‘But the antibodies that arise from an infection are the same as the antibodies arising from a vaccination, as far as these data are concerned. The latest ONS release covers the period from 5 January to 1 February this year.
‘Though the numbers of vaccinated people aged 70-74 and 75-79 were increasing rapidly over that period, the average proportion of those age groups that would have been vaccinated was much lower than for people aged 80 and over.’
He added: ‘It must be this vaccination effect that explains the very large proportion on people in England in the 80+ age group that have antibodies to the virus – almost half of them.
‘NHS data for England indicate that about a quarter of the 80+ age group had been vaccinated at the start of the period 5 January-1 February, rising to about 90 per cent by the end of the period.
‘Given that it takes a couple of weeks for the vaccine to take effect, so that antibodies would not be detectable immediately, that fits in with the proportion of this age group that had antibodies according to the ONS survey.
‘Some people in this age group would have antibodies from a previous infection, but most will have got them from vaccination. In next month’s antibody data, we should see the percentages with antibodies in the slightly younger age groups increasing a lot, and the antibody prevalence will continue to move down the age scale as vaccinations are given to more and more younger people.’
It comes after SAGE experts predicted as many as four in 10 people in Britain have already got some level of immunity to Covid-19 from either catching the coronavirus or having a vaccine.
The prediction was made in a paper presented to the Government’s top scientific advisers on January 27.
SPI-M-O, a panel that includes Professor ‘Lockdown‘ Neil Ferguson, said in the document: ‘Current estimates are that 20-40 per cent of the population have experienced a primary infection or been vaccinated.’
This suggests that those people have developed some level of protection against developing Covid-19 and this could, in theory, slow down future outbreaks.
They point out, however, that actual immunity may be lower because it can weaken over time. People who were infected a long time ago and didn’t get very ill, for example, may lose their immunity, as may elderly people who don’t make as much of an immune response.
Those who were sick recently or who get very ill, as well as people who have been vaccinated, are likely to be immune at least to severe disease, if not all infection, but scientists still don’t fully understand how often people catch it twice.
Immunity, however, may not protect people against the mutated South African variant of the virus which has been diagnosed more than 200 times in Britain.
A separate study given to SAGE claims this variant, which changes the shape of the virus’s outer spike protein so that immunity to older versions of the virus is less effective, ‘evades 21 per cent of previously acquired immunity’.
This raises concerns about how much life can return to normal after the vaccination programme as measures may need to continue to stop this variant taking over, if it will truly be able to infect a fifth of people who have been vaccinated.