Covid antibody levels have stopped rising in older people, as official figures show Britain may still be way off herd immunity.
More than half of all adults tested positive for virus-fighting antibodies in the week ending March 28 — but the figure is unchanged on the last update a fortnight ago.
And rates are actually falling among over-65s, with millions still waiting for their top-up jab.
Scientists say antibody levels dip naturally after peaking in the weeks following an infection or first vaccine, and that people may not have detectable antibodies now even if they did so earlier in the year.
But the Office for National Statistics, which tracks the levels of immunity across the UK, insisted ‘this does not mean a person has no protection against Covid’ because the immune system does not rely on antibodies to fight diseases.
The ONS surveillance project today revealed 54.9 per cent of adults have signs of immunity against the virus, rising to more than 80 per cent among those aged 64 to 73.
But every age group over 65 saw their coverage decline after levels peaked at the beginning of March.
Scientists say the 55 per cent nationwide will not be enough to offer herd immunity, which could stop the virus spreading, because this is likely to require three quarters of people to be immune to infection.
But the figures may be lower than actual levels of immunity, with the data not going up to a recent enough date to account for top-up jabs. While most people develop antibodies after their first vaccine, some don’t until their second.
Bristol University’s Professor Oliver Johnson said in a tweet: ‘I think this may put herd immunity arguments to bed for a few more weeks.’
A major Office for National Statistics (ONS) testing survey today showed 54.9 per cent of adults in England had Covid antibodies — which show if someone has gained immunity from either having the vaccine or the virus — at the end of March
The age groups with the highest antibody levels in England were 65- to 69-year-olds (84.5 per cent) and 70- to 74-year-olds (82.4 per cent), though both were beginning to see falls by the end of March
The huge immunity coverage is partly a result of the country’s vaccine drive, with more than 32.2million people now having had at least one jab – over half of adults.
Prime Minister Boris Johnson yesterday announced all over-50s, the clinically vulnerable and health and social care workers have now been offered a vaccine.
The ONS report is based on random blood tests of around 30,000 adults.
It said: ‘Weekly data show a reduction in antibody positivity rates among older individuals in recent weeks, likely because the data do not yet show the impact of second doses of Covid vaccinations.
‘Daily modelled antibody estimates by single year of age also show this decline, but the detection of antibodies alone is not a precise measure of the immunity protection given by vaccination.’
The report estimates 54.9 per cent of adults in England had Covid antibodies — which show if someone has some form of immunity from either having the vaccine or the virus — at the end of March.
Antibodies were higher than in Northern Ireland (54.5 per cent), Wales (49.1 per cent) or Scotland (46.0 per cent).
Scientists warn not to draw strong conclusions between countries because sample sizes are too small in the other nations.
Regionally in England, the areas with the highest antibody rates from March 22 to March 28 were the West Midlands (59 per cent) and North West (58.6 per cent).
The lowest rate was in the South East, where 51.9 per cent of people tested positive for antibodies, and the South West, where 52.5 per cent did.
London had an above average antibody rate of 55.4 per cent, despite having a significantly lower uptake of the vaccine.
The age groups with the highest antibody levels in England were 65- to 69-year-olds (84.5 per cent) and 70- to 74-year-olds (82.4 per cent), though both were beginning to see falls by the end of March.
NINE OUT OF 10 OVER-80s HAVE COVID ANTIBODIES SIX WEEKS AFTER FIRST JAB
Nine out of 10 people over 80 still had strong signs of coronavirus immunity six weeks after their first vaccine dose, a study has found.
The latest research by the University of Birmingham adds to evidence that the Covid vaccines are successful in the real world and work for elderly people who notoriously have weaker immune systems and respond less well to vaccines.
It found that the long-term white blood cell response were less good after a single dose of Pfizer than after AstraZeneca, but this is boosted after the second jab.
Dr Helen Parry and Professor Paul Moss, who did the research, said understanding what happens after one dose gives an idea of what protection people have now.
Out of 32.3million people vaccinated across the UK, only 7.9million have had their second jab because of a policy to stretch the gap between them to 12 weeks.
This study shows that most people show signs of long-lasting protection from the virus even if they don’t get a second dose within three weeks as people did in trials.
Testing the blood of 165 people for Covid antibodies found that 93 per cent of people had them five to six weeks after their first Pfizer jab, and 87 per cent after AstraZeneca.
‘These vaccines are equivalent in producing protection after one dose,’ Professor Moss said.
‘They are equivalent and both vaccines are good.’
Antibody levels were increasing in all age groups from 25 to 65 and over-75 were still seeing levels above 77 per cent, with second vaccine doses expected to top up levels further in the coming weeks.
Reviewing the survey, Kevin McConway, a statistician at the Open University said a reason for the slightly lower levels seen in older age groups is because antibody levels tend to decrease over time.
He said: ‘One reason for declines in antibody positivity in some older age groups may be because some people’s antibody levels, that were positive soon after their first vaccine dose, will have fallen below the level at which antibodies can be detected.
‘There’s some evidence in the oldest groups that levels might be beginning to rise again, which may well be because more of them have had a second dose and enough time has passed after that second dose for antibodies to increase.’
Professor McConway said ‘a lot is still unknown’ about how long immunity lasts for and how antibody levels change over time.
He also added that ‘antibodies aren’t the whole story on immunity’ and there are other forms of protection the body develops to the virus.
‘It’s not possible to say definitely from these results either how close we might be to a level of immunity that will keep infections strongly in check,’ he said.
The figures come after a study last week suggested Britain would pass the threshold for herd immunity on Monday.
Modelling by University College London (UCL) suggested 73.4 per cent of the population will have protection against Covid by April 12.
The figures outdo pessimistic estimations by Imperial College last week, which suggested that just 34 per cent would have the vital antibody protection by the end of last month — much less than the ONS figures today suggested.
Herd immunity is when an infectious disease stops naturally spreading in a population because enough people are protected against the disease.
Scientists disagree on what the exact herd immunity threshold is but top US medical official Dr Anthony Fauci has previously suggested it could be as high as 90 per cent.
The UK government’s Chief Scientific Advisor Sir Patrick Vallance quoted a figure of 60 per cent back in March 2020 but scientists now believe it is much higher than that because the virus is more transmissible than previously thought.
Imperial College’s results formed part of data by SPI-M – whose calculations feed into the Scientific Advisory Group on Emergencies (SAGE).
Documents published by SAGE suggest that lifting lockdown curbs fully in June could lead to more than a thousand deaths a day this summer and push the NHS to the brink again.
But UCL’s data suggests Britain could be well on its way to lifting lockdown fully by June 21, the date set out in Boris Johnson’s roadmap out of lockdown.