Seroprevalence, Waning and Correlates of Anti-SARS-CoV-2 IgG Antibodies in Tyrol, Austria: Large-Scale Study of 35,193 Blood Donors Conducted between June 2020 and September 2021

  1. Anita Siller
  2. Lisa Seekircher
  3. Gregor A. Wachter
  4. Manfred Astl
  5. Lena Tschiderer
  6. Bernhard Pfeifer
  7. Manfred Gaber
  8. Harald Schennach
  9. Peter Willeit

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Abstract

There is uncertainty about the seroprevalence of anti-SARS-CoV-2 antibodies in the general population of Austria and about the waning of antibodies over time. We conducted a seroepidemiological study between June 2020 and September 2021, enrolling blood donors aged 18–70 years across Tyrol, Austria (participation rate: 84.0%). We analyzed serum samples for antibodies against the spike or the nucleocapsid proteins of SARS-CoV-2. We performed a total of 47,363 samples taken from 35,193 individuals (median age, 43.1 years (IQR: 29.3–53.7); 45.3% women; 10.0% with prior SARS-CoV-2 infection). Seroprevalence increased from 3.4% (95% CI: 2.8–4.2%) in June 2020 to 82.7% (95% CI: 81.4–83.8%) in September 2021, largely due to vaccination. Anti-spike IgG seroprevalence was 99.6% (95% CI: 99.4–99.7%) among fully vaccinated individuals, 90.4% (95% CI: 88.8–91.7%) among unvaccinated individuals with prior infection and 11.5% (95% CI: 10.8–12.3%) among unvaccinated individuals without known prior infection. Anti-spike IgG levels were reduced by 44.0% (95% CI: 34.9–51.7%) at 5–6 months compared with 0–3 months after infection. In fully vaccinated individuals, they decreased by 31.7% (95% CI: 29.4–33.9%) per month. In conclusion, seroprevalence in Tyrol increased to 82.7% in September 2021, with the bulk of seropositivity stemming from vaccination. Antibody levels substantially and gradually declined after vaccination or infection.

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  1. Version published to 10.3390/v14030568
  2. ScreenIT

    SciScore for 10.1101/2021.12.27.21268456: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsIRB: Ethical statement: The present study was approved by the ethics committee of the Medical University of Innsbruck (no. 1352/2021).
    Sex as a biological variableSecond, to investigate differences by population subgroups, we fitted multivariable regression models that included the variables age (<25 vs. ≥25 years), sex (males vs. females), smoking (current vs. never/ex-smokers), body mass index (≥25 vs. <25 kg/m2), prior SARS-CoV-2 infection (yes vs. no) based on complete case analysis.
    RandomizationIn specific, we used (i) a generalised estimating equation with a logit link function, a binomial distribution family, and an independent variance structure to test for differences in seroprevalence among unvaccinated individuals, and (ii) a linear mixed model with a random intercept to test for differences in antibody levels after full vaccination.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    First, between 8 June 2020 and 31 March 2021, we assessed samples for anti-SARS-CoV-2 IgG antibodies targeting the nucleocapsid protein (“anti-N IgG”) using the Abbott SARS-CoV-2 IgG chemiluminescent microparticle immunoassay analysed on the Alinity i instrument (Abbott Ireland, Sligo, Ireland).
    “anti-N IgG”
    suggested: None
    Second, between 19 March 2021 and 30 September 2021, we assessed samples for anti-SARS-CoV-2 IgG antibodies targeting the spike protein (“anti-S IgG”) using the Abbott SARS-CoV-2 IgG II chemiluminescent microparticle immunoassay analysed on the Alinity i instrument.
    “anti-S IgG”
    suggested: None
    The switch to the anti-S IgG assay was done because the assay allows quantification of absolute antibody levels (in BAU/mL) and detects anti-SARS-CoV-2 IgG antibodies elicited via vaccination.
    anti-S IgG
    suggested: None
    Statistical analyses: The primary analysis quantified seroprevalence of anti-SARS-CoV-2 IgG antibodies for each of the months between June 2020 and September 2021 and is presented together with Agresti-Coull 95% CIs.
    anti-SARS-CoV-2 IgG
    suggested: None
    Software and Algorithms
    SentencesResources
    First, between 8 June 2020 and 31 March 2021, we assessed samples for anti-SARS-CoV-2 IgG antibodies targeting the nucleocapsid protein (“anti-N IgG”) using the Abbott SARS-CoV-2 IgG chemiluminescent microparticle immunoassay analysed on the Alinity i instrument (Abbott Ireland, Sligo, Ireland).
    Abbott
    suggested: (Abbott, RRID:SCR_010477)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    The study we presented herein has several important strengths and limitations. With data on 35,193 participants with 47,363 analysed samples, our study was adequately powered to reliably quantify time- and region-specific seroprevalence. Furthermore, because a subset of participants donated blood repeatedly, we gained important insight into the dynamics of antibody levels over time. Also, while the eligibility criteria for blood donation restricted our study sample to healthy individuals aged 18-70 years, the age- and sex-structure of our study sample was in close agreement with the general population, thereby supporting the generalisability of our findings to these age groups. Still, when interpreting our seroprevalence estimates, it is crucial to take into account that vaccine coverage among children and adolescents who constitute 17.4% of the population in Tyrol is much lower and therefore seroprevalence across all age groups is expected to be lower. Limitations of our study include (i) the availability of anti-N IgG antibody measurements only up to March 2021 (precluding a clear differentiation of infection- and vaccination-induced seropositivity) and (ii) lack of detailed data on the vaccination regimen (i.e. vaccination dates and vaccine type) because of time constraints at the blood donation centres.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

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  3. Version published to 10.1101/2021.12.27.21268456v1 on medRxiv