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expert reaction to the latest fortnightly release on the COVID-19 Infection Survey looking at antibody and vaccination data for the UK, 21 July 2021

The Office for National Statistics (ONS) have released the latest report from the COVID-19 infection survey, looking at antibody and vaccination data for the UK.


Dr Julian Tang, Honorary Associate Professor/Clinical Virologist, Respiratory Sciences, University of Leicester, said:

“Generally, I don’t comment too much on these ONS SARS-COV-2 antibody results – as they need to be interpreted with care – because:

“- they don’t tell you how much antibody (i.e. what levels) people have.  We know that the delta (Indian) and beta (South African) variants can cause infection in those with lower levels of antibodies due to their partial vaccine escape abilities:;;  The same is true but to a lesser extent for the alpha (Kent) and gamma (Brazilian) variants.

“- all the current vaccines were designed to the original Wuhan virus strain – they are not specific to the different variants above that we see now – so the presence of vaccine-induced or natural antibodies alone does not mean that they will necessarily protect you against specific variants – this could be partly why we are still seeing COVID-19 cases surging despite the ongoing vaccine rollout.

“- the antibody assays vary considerably – using different virus protein targets to capture patient antibodies.  Some of these assays do not capture S protein antibodies – which are the ones that are most effective at neutralising the virus.  So whilst you may have detectable antibodies, as reported in the ONS data, this data doesn’t tell you which type of antibodies you have.  For example in this paper comparing 4 different high throughout commercial antibody assays: two assays (Abbott and Roche) target the N (nucleiocapsid) protein, whereas two others (DiaSorin and Siemens) target the S protein.  You will only have the N protein antibody if you have had natural infection or have received one of the inactivated whole virus vaccines, like the Chinese CoronaVac:

“So whilst this ONS data looks very encouraging it would be more useful to have some idea of the average concentration of these antibodies, as well as the assays used in the testing, which can then also indicate exactly to which viral proteins this antibody data applies (S or N antibodies, for example).”


Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia, said:

“Today’s report from the ONS on antibody results are an important contribution to the current debate about the optimal time to lift lockdown.  Now when we are approaching 90% of the adult population having had at least one dose there still remains important sections of society yet to be immunised or later in the year when we may have been able to increase immunization rate somewhat more.  This data covers the period up to the 4th July and as has been obvious average daily case numbers have increased by over 50% since then.  But given that it takes about 7 to 10 days after either natural infection or immunisation for antibody levels to become positive, any person positive on 4th July would have been immunised or had an infection before 27th June and we are seeing infection rates now about twice what we were seeing in late June.

“Probably the most relevant data concerns antibody and vaccine uptake by age groups.

“The first important issue is that in the older age groups it does appear that antibody prevalence is starting to decline.  This is not surprising in that it is well known that Ab levels to spike protein do decline over time with a half-life of about 108 days and neutralising antibody levels are a good proxy for vaccine effectiveness  News reports from Israel over the past week are suggesting that the effectiveness of their vaccination campaign may already be waning  The relevance of this issue is in whether or not it is better to lift lockdown now or later when more people will have been vaccinated, though it remains highly uncertain what proportion of currently unvaccinated adults would eventually take up the offer.  If we wait too long then we will be seeing decreasing effectiveness of the existing vaccine campaign especially in our more vulnerable age groups.  The likelihood that vaccine effectiveness wanes over months rather than years is another reason why we will never achieve herd immunity.  As has been stated repeatedly by amongst others Chris Whitty, the heads of the WHO and European Centre for Disease Control SARS-CoV-2 is here to stay, probably for decades, to come and we can all expect to experience repeat infections throughout life, though with repeat infections being much less severe.

“The second important point is in the younger age groups.  In the 16-24 age group over 2/3rd of people already have antibody and so have some degree of immunity whether from vaccine or natural infection.  Given the time it takes for antibody to develop at least half of those people positive would have acquired antibody from natural infection.  Given that infection in this age group have been increasing in recent weeks and at least some would also have had a vaccine as well we would expect levels to be higher.  But looking at the 16 and 17 year olds (contained in the additional data files) almost 40% were antibody positive.  Accounting for loss of antibody in people who may have had a natural infection early in the pandemic and high infection rate in these groups in more recent weeks, this means that in this age group and probably all teenagers getting on for half will have already had their first infection and even though they may get repeat infections as in vaccinated individuals they are less likely to suffer severe disease.

“Although not all adults have had vaccine, many others, especially in younger age groups, will still have some degree of protection from a prior infection.  Taking all this together my view is that this supports the government’s decision to open up society now at the start of the summer holidays and delaying this would likely lead to a more dangerous autumn/winter peak due to waning vaccine induced immunity prior to an expected booster campaign in the autumn.”


Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“The latest fortnightly ONS release on antibodies and vaccination, based on their Covid-19 Infection Survey (CIS), takes the data up to the week 28 June-4 July.  The data are likely to be of high quality, because they come from a survey of a representative sample of households across the UK, and are processed statistically to improve the representativeness of the results even more.  Generally the figures on antibodies show an increase in the percentage of adults who would test positive for antibodies, across all four UK countries, compared to the position in the previous ONS bulletin a fortnight ago.  The rate of increase is levelling off a bit, but that’s to be expected when it has got as high as it is (particularly in the older age groups).

“Across all four countries and in all the English regions, the proportion who would test positive for antibodies to the virus that can cause Covid-19 is around nine in ten.  There’s a bit of variation between countries and regions, but not a lot.  The antibody test used in this study doesn’t distinguish between antibodies arising because some has been infected, and antibodies arising from vaccination.  There are differences by age in the proportion who would test positive for antibodies, as you might expect given that vaccine distribution was mostly organised by age, with older people first.  In the second youngest age group that ONS use in these bulletins, age 25-34, the proportion who would test positive is now about nine in ten, or higher, in three of the four UK countries, and only a little lower in Northern Ireland.  In all the age groups older than that, the rate is even higher, in some cases over 99%.  That’s impressive.  However, the positivity rate is lower in the youngest age group, 16-24.  Across the four countries, it is between 6 and 7 in every 10 people, meaning that 3 or 4 in every 10 do not yet have antibodies.  That’s also not surprising, given that, for most in that age group, vaccines have only just become available in the past few weeks, and it takes a little time after vaccination for antibodies to become detectable.  In that youngest age group, the proportion who have been vaccinated (up to the week ending 4 July) is about half in England, and a bit less than that in the other UK countries (only just over a third in Wales).  So there’s some way to go – and we’ve got to remember that those aged 16 and 17 are not currently supposed to be vaccinated, under current guidelines, unless they themselves, or someone they live with, is specially vulnerable.  (Indeed, that applies to younger children too, but 16 and 17 year olds are in the 16-24 age groups that ONS use for this analysis.)”



All our previous output on this subject can be seen at this weblink:



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.”

None others received.

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