Vaccine-surveillance-report

 < 

Vaccine-surveillance-report.. 

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. 

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) 

•Roche N (infection) 

•- vaccination introduced

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 .

week number (12-week period mid point) 

London 

North East & Yorks 

East of England 

Midlands

South West 

North West 

South East 

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

NHS region: 

Weeks 21-32; 

Weeks 33-40 

•East of England :

13.3%(12.1%-14.6%) ;

15.7%(14.1%-17.3%) 

•London :

25.0%(23.5%-26.6%) ;

27.1%(25.2%-29.0%) 

•Midlands :

16.2%(15.0%-17.6%) ;

19.1%(17.2%-21.1%) 

•North East and Yorkshire :

15.7%(14.3%-17.1%) ;

19.3%(17.6%-21.2%) 

•North West :

20.7%(19.1%-22.4%) ;

25.9%(23.9%-28.1%) 

•South East :

12.9%(11.7%-14.2%) ;

14.9%(13.4%-16.6%) 

•South West :

9.4%(8.3%-10.6%) ;

12.8%(11.3%-14.5%).

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

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.

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

Age group ; Weeks 21-32 :

17-29 ; 24.1%(22.6%-25.8%) 

30-39 ; 18.4%(17.3%-19.7%) 

40-49 ; 17.6%(16.5%-18.8%) 

50-59 ; 16.4%(15.4%-17.4%) 

60-69 ; 11.0%(10.0%-12.0%) 

70-84 ; 7.2%(6.0%-8.7%) 

Weeks 33-40 :

28.8%(26.6%-31.0%) 

23.6%(22.0%-25.3%) 

19.9%(18.5%-21.5%) 

18.4%(17.1%-19.7%) 

13.4%(12.2%-14.8%) 

7.9%(6.4%-9.7%)

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 overallI 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 (ii) 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.

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.

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.

Vaccine-surveillance-report... 

COVID-19 vaccine surveillance report-week 42 

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 

5. Whitaker H and others. 'Pfizer-BioNTech and Oxford AstraZeneca COVID-19 vaccine effectiveness and immune response among individuals in clinical risk groups' 

6. Amirthalingham G and others.'Higher serological responses and increased vaccine effectiveness demonstrate the value of extended vaccine schedules in combatting COVID-19 in England' medRxiv 2021 

7. Lopez Bernal J and others. 'Effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines on COVID-19-related symptoms, hospital admissions, and mortality in older adults in England: test negative case-control study' British Medical Journal 2021: volume 373, n1,088 

8. Vasileiou E and others. 'Effectiveness of first dose of COVID-19 vaccines against hospital admissions in Scotland: national prospective cohort study of 5.4 million people' 2021 

9.Hyams C and others. 'Effectiveness of BNT162b2 and ChAdOx1 nCoV-19 COVID-19 vaccination at preventing hospitalisations in people aged at least 80 years: a test-negative, case-control study' Lancet Infectious Diseases 2021 Ismail SA and others. 'Effectiveness of BNT162b2 mRNA and ChAdOx1 adenovirus vector COVID-19 vaccines on risk of hospitalisation among older adults in England: an observational study using surveillance data' Public Health England Preprints 2021 

10. Ismail SA and others. 'Effectiveness of BNT162b2 mRNA and ChAdOx1 adenovirus vector COVID-19 vaccines on risk of hospitalisation among older adults in England: an observational study using surveillance data' Public Health England Preprints 2021.

11. Lopez Bernal J and others. 'Effectiveness of BNT162b2 mRNA vaccine and ChAdOx1 adenovirus vector vaccine on mortality following COVID-19' Public Health England Preprints 2021 

12. Pritchard E and others. 'Impact of vaccination on SARS-CoV-2 cases in the community: a population-based study using the UK's COVID-19 Infection Survey' medRxiv 2021:2021.04.22.21255913 

13. Hall VJ and others. 'COVID-19 vaccine coverage in health-care workers in England and effectiveness of BNT162b2 mRNA vaccine against infection (SIREN): a prospective, multicentre,cohort study' Lancet 2021 

14.Shrotri M and others. 'Vaccine effectiveness of the first dose of ChAdOx1 nCoV-19 and BNT162b2 against SARS-CoV-2 infection in residents of long-term care facilities in England (VIVALDI): a prospective cohort study' Lancet Infectious Diseases 2021 

27 

COVID-19 vaccine surveillance report - week 42 

15. Menni C and others. Vaccine side-effects and SARS-CoV-2 infection after vaccination in users of the COVID Symptom Study app in the UK: a prospective observational study' Lancet Infectious Diseases 2021 

16. Harris RJ and others. 'Effect of Vaccination on Household Transmission of SARS-CoV-2 in England' New England Journal of Medicine 2021 

17. v Shah AS and others. 'Effect of vaccination on transmission of COVID-19: an observational study in healthcare workers and their households.' medRxiv 2021: 2021.03.11.21253275