COVID-19 vaccine surveillance report Week 42/ Poziom przeciwciał, niższy u zaszczepionych (trwale)

UK Health  Security Agency

COVID-19 vaccine surveillance report  Week 42

Rząd Wielkiej Brytanii oficjalnie przyznaje, że szczepionki uszkodziły
naturalny układ odpornościowy tych, którzy zostali zaszczepieni
podwójnie. Rząd Wielkiej Brytanii przyznał, że po podwójnym
zaszczepieniu już nigdy nie będziesz w stanie uzyskać pełnej
naturalnej odporności na warianty Covid – lub prawdopodobnie na
jakikolwiek inny wirus. Zobaczmy więc jak zaczyna się „prawdziwa”
pandemia! W 42. tygodniu „Raportu z nadzoru szczepień przeciw
COVID-19” brytyjski Departament Zdrowia przyznaje na stronie 23, że
„poziom przeciwciał N wydaje się być niższy u osób zakażonych po dwóch
dawkach szczepienia”. Dalej mówi się, że ten spadek przeciwciał jest
zasadniczo trwały. Co to znaczy? Wiemy, że szczepionki nie zapobiegają
zakażeniu ani przenoszeniu wirusa (w rzeczywistości raport w innym
miejscu pokazuje, że zaszczepione osoby dorosłe są znacznie bardziej
narażone na zakażenie niż osoby nieszczepione). Brytyjczycy odkryli
teraz, że szczepionka zaburza zdolność organizmu do wytwarzania
przeciwciał po zakażeniu nie tylko przeciwko białku kolca, także
przeciwko innym częściom wirusa. W szczególności wydaje się, że
zaszczepione osoby nie wytwarzają przeciwciał przeciwko białku
nukleokapsydu, otoczce wirusa, która jest kluczową częścią odpowiedzi
u osób nieszczepionych. Na dłuższą metę osoby zaszczepione są znacznie
bardziej podatne na wszelkie mutacje w białku kolczastym, nawet jeśli
zostały już zakażone i wyleczone raz lub więcej. Z drugiej strony,
osoby niezaszczepione, po jednokrotnym naturalnym zakażeniu uzyskują
trwałą, lub bliską temu, odporność na wszystkie szczepy domniemanego
wirusa.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1027511/Vaccine-surveillance-report-week-42.pdf

Summary...................................................................................................................................................... 3

Vaccine effectiveness................................................................................................................................ 3

Population impact....................................................................................................................................... 3

Vaccine effectiveness................................................................................................................................ 4

Effectiveness against symptomatic disease........................................................................................... 4

Effectiveness against hospitalisation...................................................................................................... 5

Effectiveness against mortality................................................................................................................. 5

Effectiveness against infection................................................................................................................. 5

Effectiveness against transmission.......................................................................................................... 6

Population impact....................................................................................................................................... 8

Vaccine coverage....................................................................................................................................... 8

Vaccination status.................................................................................................................................... 11

Vaccine impact on proportion of population with antibodies to COVID-19..................................... 19

Summary of impact on hospitalisations, infections and mortality...................................................... 26

References................................................................................................................................................ 27

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COVID-19 vaccine surveillance report - week 42

Summary

Four coronavirus (COVID-19) vaccines have now been approved for use in the UK. Rigorous clinical trials have been undertaken to understand the immune response, safety profile and efficacy of these vaccines as part of the regulatory process. Ongoing monitoring of the vaccines as they are rolled out in the population is important to continually ensure that clinical and public health guidance on the vaccination programme is built upon the best available evidence.

UK Health Security Agency, UKHSA, formerly Public Health England (PHE), works closely with the Medicines and Healthcare Regulatory Agency (MHRA), NHS England, and other government, devolved administration and academic partners to monitor the COVID-19 vaccination programme. Details of the vaccine surveillance strategy are set on the page COVID-19: vaccine surveillance strategy Q). As with all vaccines, the safety of COVID-19 vaccines is continuously being monitored by the MHRA. They conclude that overall, the benefits of COVID-19 vaccines outweigh any potential risks (2).

Vaccine effectiveness

Several studies of vaccine effectiveness have been conducted in the UK which indicate that 2 doses of vaccine are between 65 and 95% effective at preventing symptomatic disease with COVID-19 with the Delta variant, with higher levels of protection against severe disease including hospitalisation and death. There is some evidence of waning of protection against infection and symptomatic disease over time, though protection against severe disease remains high in most groups at least 5 months after the second dose.

Population impact

The impact of the vaccination programme on the population is assessed by taking into account vaccine coverage, evidence on vaccine effectiveness and the latest COVID-19 disease surveillance indicators. Vaccine coverage tells us about the proportion of the population that have received 1 and 2 doses of COVID-19 vaccines. By 10 October 2021, the overall vaccine uptake in England for dose 1 was 65.5% and 60.4% for dose 2. In line with the programme rollout, coverage is highest in the oldest age groups.

We present data on COVID-19 cases, hospitalisations and deaths by vaccination status.

Based on antibody testing of blood donors, 98.0% of the adult population now have antibodies to COVID-19 from either infection or vaccination compared to 18.7% that have antibodies from infection alone.

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COVID-19 vaccine surveillance report - week 42

Vaccine effectiveness

Large clinical trials have been undertaken for each of the COVID-19 vaccines approved in the UK which found that they are highly efficacious at preventing symptomatic disease in the populations that were studied. The clinical trials have been designed to be able to assess the efficacy of the vaccine against laboratory confirmed symptomatic disease with a relatively short follow up period so that effective vaccines can be introduced as rapidly as possible. Nevertheless, understanding the effectiveness against different outcomes (such as severe disease and onwards transmission), effectiveness in different subgroups of the population and understanding the duration of protection are equally important in decision making around which vaccines should be implemented as the programme evolves, who they should be offered to and whether booster doses are required.

Vaccine effectiveness is estimated by comparing rates of disease in vaccinated individuals to rates in unvaccinated individuals. Below we outline the latest real-world evidence on vaccine effectiveness from studies in UK populations. We focus on data related to the Delta variant which is currently dominant in the UK. The findings are also summarised in Table 1.

Effectiveness against symptomatic disease

Vaccine effectiveness against symptomatic COVID-19 has been assessed in England based on community testing data linked to vaccination data from the National Immunisation Management System (NIMS), cohort studies such as the COVID Infection Survey and GP electronic health record data. After 2 doses, observed vaccine effectiveness against symptomatic disease with the Delta variant reaches approximately 65 to 70% with AstraZeneca Vaxzevria and 80 to 95% with Pfizer-BioNTech Comirnaty and Moderna Spikevax (3, 4) Vaccine effectiveness is generally slightly higher in younger compared to older age groups. With both Vaxzevria and Comirnaty, there is evidence of waning of protection over time, most notably among older adults. There is not yet enough follow-up with Spikevax to assess waning (3).

Data (based primarily on the Alpha variant) suggest that in most clinical risk groups, immune response to vaccination is maintained and high levels of VE are seen with both the Pfizer and AstraZeneca vaccines. Reduced antibody response and vaccine effectiveness were seen after one dose of vaccine among the immunosuppressed group, however, after a second dose the reduction in vaccine effectiveness is smaller (5).

Analyses by dosing interval suggest that immune response to vaccination and vaccine effectiveness against symptomatic disease improves with a longer (greater than 6 week interval) compared to a shorter interval of 3 to 4 weeks (6, 3)

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COVID-19 vaccine surveillance report - week 42

Effectiveness against hospitalisation

Several studies have estimated vaccine effectiveness against hospitalisation in older ages, all of which indicate higher levels of protection against hospitalisation with all vaccines against the Alpha variant (7, 8, 9, 10). Effectiveness against hospitalisation of over 90% is also observed with the Delta variant with all 3 vaccines (3). In most groups there is relatively limited waning of protection against hospitalisation over a period of at least 5 months after the second dose. Greater waning appears to occur among those in clinical risk groups (3).

Effectiveness against mortality

High levels of protection (over 90%) are also seen against mortality with all 3 vaccines and against both the Alpha and Delta variants (7, 11, 3). Relatively limited waning of protection against mortality is seen over a period of at least 5 months.

Effectiveness against infection

Although individuals may not develop symptoms of COVID-19 after vaccination, it is possible that they could still be infected with the virus and could transmit to others. Understanding how effective vaccines are at preventing infection is therefore important to predict the likely impact of the vaccination programme on the wider population. In order to estimate vaccine effectiveness against infection, repeat asymptomatic testing of a defined cohort of individuals is required. Studies have now reported on vaccine effectiveness against infection in healthcare workers, care home residents and the general population (12, 13, 14, 15). With the delta variant, vaccine effectiveness against infection has been estimated at around 65% with Vaxzevria and 80% with Comirnaty (4).

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COVID-19 vaccine surveillance report - week 42

Effectiveness against transmission

As described above, several studies have provided evidence that vaccines are effective at preventing infection. Uninfected individuals cannot transmit; therefore, the vaccines are also effective at preventing transmission. There may be additional benefit, beyond that due to prevention of infection, if some of those individuals who become infected despite vaccination are also at a reduced risk of transmitting (for example, because of reduced duration or level of viral shedding). A household transmission study in England found that household contacts of cases vaccinated with a single dose had approximately 35 to 50% reduced risk of becoming a confirmed case of COVID-19. This study used routine testing data so would only include household contacts that developed symptoms and went on to request a test via pillar 2. It cannot exclude asymptomatic secondary cases or mildly symptomatic cases who chose not to request a COVID-19 test (16). Data from Scotland has also shown that household contacts of vaccinated healthcare workers are at reduced risk of becoming a case, which is in line with the studies on infection (17). Both of these studies relate to a period when the Alpha variant dominated. An analysis from the ONS Community Infection Survey found that contacts of vaccinated index cases had around 65 to 80% reduced odds of testing positive with the Alpha variant and 35 to 65% reduced odds of testing positive with the Delta variant compare to contacts of unvaccinated index cases (18).

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COVID-19 vaccine surveillance report - week 42

A summary of vaccine effectiveness evidence can be seen in Table 1.

Table 1. Summary of evidence on vaccine effectiveness against different outcomes Delta

* Estimates of initial vaccine effectiveness in the general population after a 2 dose course. This typically applies for at least the first 3 to 4 months after vaccination. For some outcomes there may be waning of effectiveness beyond this point.

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COVID-19 vaccine surveillance report - week 42

Population impact

Vaccines typically have both direct effects on those who are vaccinated and indirect effects on the wider population due to a reduced probability that people will come into contact with an infected individual. The overall impact of the vaccination programme may therefore extend beyond that estimated through vaccine effectiveness analysis.

Estimating the impact of a vaccination programme is challenging as there is no completely unaffected control group. Furthermore, the effects of the vaccination programme need to be differentiated from that of other interventions (for example, lockdowns or outbreak control measures), changes in behaviour and any seasonal variation in COVID-19 activity.

UKHSA and other government and academic partners monitor the impact of the of the vaccination programme on levels of COVID-19 antibodies in the population and different disease indicators, including hospitalisations and mortality. This is done through population- based testing and through modelling which combines vaccine coverage rates in different populations, estimates of vaccine effectiveness and disease surveillance indicators.

Vaccine coverage

Please note that in order to undertake preparatory work prior to a change in the definition of age-cohorts and to ensure alignment across publications of weekly data, data on vaccine uptake are not being updated this week. Normal publication will resume next week. Daily figures on uptake can be found on the COVID-19 Data Dashboard.

The data in this week’s report covers the period from 8 December 2020 to 10 October 2021 (week 40) (Figure 1). It shows the provisional number and percentage of people in England who have had received 1 dose or 2 doses of a COVID-19 vaccination by age group and week since the start of the programme.

Up to 30 September 2021 84,122 women of child-bearing age in England (under 50) who reported that they were pregnant or could be pregnant at the time, received at least one dose of COVID-19 vaccination and of these, 67,144 have received their second dose. This is in response to the self-reported pre-screening question "Are you or could you be pregnant?”. The true number of pregnant women who have had a COVID-19 vaccination is likely to be greater than this.

Please note that pregnant women are not a separate priority group as defined by JCVI who have advised that "women who are pregnant should be offered vaccination at the same time as non-pregnant women, based on their age and clinical risk group” therefore comparing vaccine uptake in pregnant women to other vaccination programmes is not currently appropriate. The MHRA closely monitors the safety of COVID-19 vaccine exposures in pregnancy, including Yellow Card reports for COVID-19 vaccines used in pregnancy, for the latest information please see the webpage Coronavirus vaccine - weekly summary of Yellow Card reporting.

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% vaccine uptake

COVID-19 vaccine surveillance report - week 42

Figure 1. Cumulative weekly vaccine uptake by age

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$     75 to under 80

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% vaccine uptake

COVID-19 vaccine surveillance report - week 42

1. b) Dose 2

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COVID-19 vaccine surveillance report - week 42

Vaccination status

Vaccination status of COVID-19 cases, deaths and hospitalisations by week of specimen date over the past 4 weeks up to week 41 (up to 17 October 2021) are shown in Table 2 to 4 and Figure 2.

Please note that data on vaccine uptake are not being updated this week, and as such the population sizes used to calculate rates relate to last week’s data.

Methods

COVID-19 cases and deaths identified through routine collection from the Second Generation Surveillance System (SGSS) and from UKHSA EpiCell's deaths data as described here, were linked to the National Immunisation Management System (NIMS) to derive vaccination status, using an individual’s NHS number as the unique identifier.

Attendance to emergency care at NHS trusts was derived from the Emergency Care DataSet (ECDS) managed by NHS Digital. The same data source was used to identify COVID-19 cases where the attendance to emergency care resulted in admission to an NHS trust.

ECDS is updated weekly, and cases are linked to these data twice weekly. Data from ECDS are subject to reporting delays as, although NHS trusts may update data daily, the mandatory deadline for submission is by the 21st of every month. This means that for weeks immediately following the 21st of a month, numbers may be artificially low and are likely to be higher in later versions of the report.

Data from ECDS also only report on cases who have been presented to emergency care and had a related overnight patient admission and do not show those who are currently in hospital with COVID-19. As such, it is not appropriate for use for surveillance of those currently hospitalised with COVID-19. In addition, these data will not show cases who were directly admitted as inpatients without presenting to emergency care.

The outcome of overnight inpatient admission following presentation to emergency care, was limited to those occurring within 28 days of the earliest specimen date for a COVID-19 case.

Deaths include those who died (a) within 28 days of the earliest specimen date or (b) within 60 days of the first specimen date or more than 60 days after the first specimen date with COVID- 19 mentioned on the death certificate.

The rate of COVID-19 cases, hospitalisation, and deaths in fully vaccinated and unvaccinated groups was calculated using vaccine coverage data for each age group extracted from the National Immunisation Management Service.

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COVID-19 vaccine surveillance report - week 42

Results

The rate of a positive COVID-19 test varies by age and vaccination status. The rate of a positive COVID-19 test is substantially lower in vaccinated individuals compared to unvaccinated individuals up to the age of 29. In individuals aged greater than 30, the rate of a positive COVID-19 test is higher in vaccinated individuals compared to unvaccinated. This is likely to be due to a variety of reasons, including differences in the population of vaccinated and unvaccinated people as well as differences in testing patterns.

The rate of hospitalisation within 28 days of a positive COVID-19 test increases with age, and is substantially greater in unvaccinated individuals compared to vaccinated individuals.

The rate of death within 28 days or within 60 days of a positive COVID-19 test increases with age, and again is substantially greater in unvaccinated individuals compared to fully vaccinated individuals.

Interpretation of data

These data should be considered in the context of vaccination status of the population groups shown in the rest of this report. The vaccination status of cases, inpatients and deaths is not the most appropriate method to assess vaccine effectiveness and there is a high risk of misinterpretation. Vaccine effectiveness has been formally estimated from a number of different sources and is described earlier in this report.

In the context of very high vaccine coverage in the population, even with a highly effective vaccine, it is expected that a large proportion of cases, hospitalisations and deaths would occur in vaccinated individuals, simply because a larger proportion of the population are vaccinated than unvaccinated and no vaccine is 100% effective. This is especially true because vaccination has been prioritised in individuals who are more susceptible or more at risk of severe disease. Individuals in risk groups may also be more at risk of hospitalisation or death due to non- COVID-19 causes, and thus may be hospitalised or die with COVID-19 rather than because of COVID-19.

The case rates in the vaccinated and unvaccinated populations are crude rates that do not take into account underlying statistical biases in the data. There are likely to be systematic differences in who chooses to be tested and the COVID risk of people who are vaccinated.

These biases become more evident as more people are vaccinated and the differences between the vaccinated and unvaccinated population become systematically different in ways that are not accounted for without undertaken formal analysis of vaccine effectiveness as is made clear.

NIMS is used as a denominator because it is a database of named individuals eligible for vaccination in which there is a record of each individual’s vaccination status.

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COVID-19 vaccine surveillance report - week 42

Table 2. COVID-19 cases by vaccination status between week 38 and week 41 2021

* Individuals whose NHS numbers were unavailable to link to the NIMS

** Interpretation of the case rates in vaccinated and unvaccinated population is particularly susceptible to changes in denominators and should be interpreted with extra caution

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COVID-19 vaccine surveillance report - week 42

Table 3. COVID-19 cases presenting to emergency care (within 28 days of a positive specimen) resulting in an

overnight inpatient admission by vaccination status between week 38 and week 41 2021

* Individuals whose NHS numbers were unavailable to link to the NIMS

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COVID-19 vaccine surveillance report - week 42

Table 4. COVID-19 deaths (a) within 28 days and (b) within 60 days of positive specimen or with COVID-19 reported on death certificate, by vaccination status between week 38 and week 41 2021

(a)

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COVID-19 vaccine surveillance report - week 42

(b)

* Individuals whose NHS numbers were unavailable to link to the NIMS

** Number of deaths of people who had had a positive test result for COVID-19 and either died within 60 days of the first positive test or have COVID-19 mentioned on their death certificate

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COVID-19 vaccine surveillance report - week 42

Figure 2. Rates (per 100,000) by vaccination status from week 38 to week 41 2021

(a) COVID-19 cases

Age group

■ Vaccinated with at least 2 doses □ Unvaccinated

(b) Cases presenting to emergency care (within 28 days of a positive test) resulting in overnight inpatient admission

Age group

■ Vaccinated with at least 2 doses □ Unvaccinated

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COVID-19 vaccine surveillance report - week 42

(c) Death within 28 days of positive COVID-19 test

Age group

■ Vaccinated with at least 2 doses □ Unvaccinated

(d) Death within 60 days of positive COVID-19 test

Age group

■ Vaccinated with at least 2 doses □ Unvaccinated

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COVID-19 vaccine surveillance report - week 42

Vaccine impact on proportion of population with antibodies to COVID-19

Seroprevalence

The results from testing samples provided by healthy adult blood donors aged 17 years and older, supplied by the NHS Blood and Transplant (NHS BT collection) between weeks 35 2020 and week 40 2021 are summarised. As of week 44 2020, approximately 250 samples from each geographic NHS region are tested each week.

The COVID-19 vaccination campaign began on the 8 December 2020 (week 50) with a phased roll out by age and risk group. A booster dose was introduced from 16 September 2021 for individuals aged 50 years and over, frontline health and social care staff, individuals aged 16 to 49 with certain underlying health conditions and household contacts of immunosuppressed individuals. Booster doses are given at least 6 months after the second dose.

Please note that this section will be updated monthly. Last update was published 21 October 2021.

Seroprevalence in blood donors aged 17 years and older

The results presented here are based on testing samples with Roche nucleoprotein (N) and Roche spike (S) antibody assays.

Nucleoprotein (Roche N) assays only detect post-infection antibodies, whereas spike (Roche S) assays will detect both post-infection antibodies and vaccine-induced antibodies. Thus, changes in seropositivity for the Roche N assay reflect the effect of natural infection. Increases in seropositivity as measured by S antibody reflect both infection and vaccination. Antibody responses to both targets reflect infection or vaccination occurring at least 2 to 3 weeks previously given the time taken to generate a COVID-19 antibody response. Donors have been asked to defer donations for at least 7 full days post vaccination, and for at least 28 days post recovery if side-effects following vaccination or COVID-19 infection.

This report presents Roche N and Roche S seropositivity estimates on the same set of samples, using a 12-week rolling prevalence for national, age group and regional estimates. Seropositivity estimates are plotted using the mid-point of a 12-weekly rolling period that reduces to 8 weeks in the most recent weeks to allow for a more representative current estimate of seropositivity. Seroprevalence estimates reported are based on seropositivity which are unadjusted for the sensitivity and specificity of the assays used.

This is the first week reporting using a 12-weekly period for national and age group estimates. Previously, national and age group seropositivity was reported using a 4-week rolling period.

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COVID-19 vaccine surveillance report - week 42

National prevalence

Overall population weighted (by age group, sex and NHS region) antibody prevalence among blood donors aged 17 years and older in England was 18.7% (95% CI 17.7% to 19.8%) using the Roche N assay and 98.0% (95% CI 97.7% to 98.3%) using the Roche S assay for the period 16 August to 10 October (weeks 33 to 40 2021). 1,334 out of 7,384 were Roche N positive and 14,815 out of 15,081 samples were Roche S positive. This compares with 14.9% (95% CI 14.1% to 15.8%) Roche N seropositivity and 92.3% (95% CI 91.9% to 92.7%) Roche S seropositivity for the period of 24 May to 13 August 2021 (weeks 21 to 32 2021).

Seropositivity (weighted by region, age group and sex) varies over time. Figure 3 shows the overall 12-weekly rolling proportion seropositive over time for the Roche N and Roche S assays. Seropositivity estimates are plotted weekly using the mid-point of a rolling 12-weekly period.

Figure 3: Overall 12-weekly rolling SARS-CoV-2 antibody seroprevalence (% seropositive) in blood donors.

Roche S (infection / vaccination) ...a** Roche N (infection)       vaccination introduced

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COVID-19 vaccine surveillance report - week 42

Regional prevalence of infection over time

Seropositivity (weighted by age group and sex) using the Roche N assay which detects infection only, varies by region (Figure 4).

Figure 4: Twelve-weekly rolling SARS-CoV-2 antibody seroprevalence (% seropositive) in blood donors by region, using Roche N test; error bars show 95% confidence intervals

30

25

20

CD

> 

(/)

o

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(/)

o''

10

5

0

48 50 52                 1    3    5    7    9    11  13 15 17 19 21 23 25 27 29 31 33 35 37 39

week number (12-week period mid point)

• —if— London —if— Midlands —if— North West

—it— North East & Yorks                    —it— South West                    —it— South East

—it— East of Eng

Table 5: Roche N seropositivity (95%CI) estimates by NHS region

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COVID-19 vaccine surveillance report - week 42

Increases in Roche N seropositivity have recently been observed across all regions (Table 5) compared to the previous 12-week period.

London has consistently seen the highest Roche N seropositivity with the lowest observed in the South West.

Prevalence by age group

Seropositivity estimates by age group using the Roche N assay are presented below.

Figure 5: Population weighted 12-weekly rolling SARS-CoV-2 antibody seroprevalence (% seropositive) in blood donors from the Roche N assay by age group

17-29                      30-39

• ••*■■• 40-49 50-59 60-64            70-84

Based on testing samples using the Roche N assay (Figure 5) as a marker of infection, the highest seropositivity has consistently been observed in those aged 17 to 29 and the lowest in those aged 70 to 84.

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COVID-19 vaccine surveillance report - week 42

Table 6: Roche N seropositivity (95%CI) estimates by age group

Small increases in Roche N seropositivity have recently been observed across all age groups (Table 6) compared to the previous 12-week period. Increases in the overall COVID-19 case rates in England have been observed across all age groups and regions in week 40 (Weekly national Influenza and COVID-19 surveillance report week 41).

Roche S seropositivity in blood donors has plateaued and is now over 96% across all age groups.

Seropositivity estimates for S antibody in blood donors are likely to be higher than would be expected in the general population and this probably reflects the fact that donors are more likely to be vaccinated. Seropositivity estimates for N antibody will underestimate the proportion of the population previously infected due to (i) blood donors are potentially less likely to be exposed to natural infection than age matched individuals in the general population (ii) waning of the N antibody response over time and (iii) recent observations from UK Health Security Agency (UKHSA) surveillance data that N antibody levels appear to be lower in individuals who acquire infection following 2 doses of vaccination.

Vaccination has made an important contribution to the overall Roche S increases observed since the roll out of the vaccination programme, initially amongst individuals aged 50 years and above who were prioritised for vaccination as part of the phase 1 programme and more recently in younger adults as part of phase 2 of the vaccination programme.

Roche S levels by age group and month

The Roche S assay that the UK Health Security Agency (UKHSA) uses for serological surveillance is fully quantitative, meaning that it measures the level of antibodies in a blood sample; an antibody level above 0.8 AU/ml (approximately one IU/ml using the WHO standard) is deemed positive. The PHE and UKHSA surveillance over the past few months has found that over 97% of the population of blood donors test positive for S-antibodies, which may have resulted from either COVID-19 infection or vaccination. With such high seropositivity, it is important to look at population antibody levels in order to assess the impact of the vaccination booster programme.

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COVID-19 vaccine surveillance report - week 42

Figure 6 shows monthly categorised Roche S levels in N-antibody negative individuals by age group. Almost all tested S-antibody negative during December. In the 3 oldest age groups, the impact of first vaccine dose, then second vaccine dose, can be seen from December through June, as the profile of population antibody levels increases. Then from June through September the profile of antibody levels in these cohorts gradually decreases, consistent with waning. During October there is a small increase in percentage of donors with high antibody levels of 1000+ AU/ml for the 70 to 84 age group only, following the initiation of the booster programme. The higher profile of antibody levels in the youngest age group, is likely a result of a combination of factors including stronger immune responses in younger individuals and the higher antibody levels produced after mRNA vaccination.

Figure 7 shows categorised Roche S levels in N-antibody positive individuals, those likely to have experienced past infection. Pre-vaccination antibody levels will be influenced by time since infection, variant and severity of infection, as well as personal factors such as underlying health conditions and age. At the start of the vaccination rollout in December antibody levels typically sat within the range of 0.8 to 1000 AU/ml, after vaccination antibody levels typically exceed 1000 AU/ml. Comparing Figure 6 with Figure 7, the overall higher profile of antibody levels in those who have experienced past infection is evident; both vaccination post infection and breakthrough infection following vaccination are expected to boost existing antibody levels.

Researchers across the globe are working to better understand what antibody levels mean in terms of protection against COVID-19. Current thinking is that there is no threshold antibody level that offers complete protection against infection, but instead that higher antibody levels are likely to be associated with lower probability of infection.

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COVID-19 vaccine surveillance report - week 42

Figure 6: Categorised Roche S antibody levels by age group and month in N negative samples, December 2020 to October 2021

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<0.8 (negative) 0.8-<25 25-<250 250-<1000 1000-<2500 2500-<10000* 10000+*

0 20 40 60 80100             0 20 40 60 80 100 0 20 40 60 80 100

percent

*levels were capped at 2500 in samples taken before 11 May 2021

Figure 7: Categorised Roche S antibody levels by age group and month in N positive samples, December 2020 to October 2021

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percent

*levels were capped at 2500 in samples taken before 11 May 2021

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COVID-19 vaccine surveillance report - week 42

Summary of impact on hospitalisations, infections and mortality

UKHSA previously reported on the number of hospitalisations directly averted by vaccination. In total, around 261,500 hospitalisations have been prevented in those aged 45 years and over up to 19 September 2021.

UKHSA and University of Cambridge MRC Biostatistics Unit previously reported on the direct and indirect impact of the vaccination programme on infections and mortality. Estimates suggest that 127,500 deaths and 24,144,000 infections have been prevented as a result of the COVID- 19 vaccination programme, up to 24 September.

Neither of these models will be updated going forward. This is due to these models being unable to account for the interventions that would have been implemented in the absence of vaccination. Consequently, over time the state of the actual pandemic and the no-vaccination pandemic scenario have become increasingly less comparable. For further context surrounding this figure and for previous estimates, please see previous vaccine surveillance reports.

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References

1. Public Health England. ‘COVID-19: vaccine surveillance strategy 2021’
2. Medicines and Healthcare Products Regulatory Agency. ‘Coronavirus vaccine - weekly summary of Yellow Card reporting 2021’
3. Andrews N and others. ‘Vaccine effectiveness and duration of protection of Comirnaty, Vaxzervia and Spikevax against mild and severe COVID-19 in the UK’ Knowledge Hub 2021
4. Pouwels K and others. ‘Impact of Delta on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK’ MedRxiv 2021
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COVID-19 vaccine surveillance report - week 42

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