Time Trend in SARS-CoV-2 Seropositivity, Surveillance Detection- and Infection Fatality Ratio until Spring 2021 in the Tirschenreuth County-Results from a Population-Based Longitudinal Study in Germany

Viruses. 2022 May 27;14(6):1168. doi: 10.3390/v14061168.


Herein, we provide results from a prospective population-based longitudinal follow-up (FU) SARS-CoV-2 serosurveillance study in Tirschenreuth, the county which was hit hardest in Germany in spring 2020 and early 2021. Of 4203 individuals aged 14 years or older enrolled at baseline (BL, June 2020), 3546 participated at FU1 (November 2020) and 3391 at FU2 (April 2021). Key metrics comprising standardized seroprevalence, surveillance detection ratio (SDR), infection fatality ratio (IFR) and success of the vaccination campaign were derived using the Roche N- and S-Elecsys anti-SARS-CoV-2 test together with a self-administered questionnaire. N-seropositivity at BL was 9.2% (1st wave). While we observed a low new seropositivity between BL and FU1 (0.9%), the combined 2nd and 3rd wave accounted for 6.1% new N-seropositives between FU1 and FU2 (ever seropositives at FU2: 15.4%). The SDR decreased from 5.4 (BL) to 1.1 (FU2) highlighting the success of massively increased testing in the population. The IFR based on a combination of serology and registration data resulted in 3.3% between November 2020 and April 2021 compared to 2.3% until June 2020. Although IFRs were consistently higher at FU2 compared to BL across age-groups, highest among individuals aged 70+ (18.3% versus 10.7%, respectively), observed differences were within statistical uncertainty bounds. While municipalities with senior care homes showed a higher IFR at BL (3.0% with senior care home vs. 0.7% w/o), this effect diminished at FU2 (3.4% vs. 2.9%). In April 2021 (FU2), vaccination rate in the elderly was high (>77.4%, age-group 80+).

Keywords: SARS-CoV-2; case fatality ratio; elderly; infection fatality ratio; longitudinal; population-based; senior care homes; seroprevalence; surveillance detection ratio; vaccination.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Antibodies, Viral
  • COVID-19* / diagnosis
  • COVID-19* / epidemiology
  • Germany / epidemiology
  • Humans
  • Longitudinal Studies
  • Prospective Studies
  • SARS-CoV-2*
  • Seroepidemiologic Studies


  • Antibodies, Viral

Grants and funding

This work was supported by the Bavarian States Ministry of Science and Arts (TiKoCo-19 and ForCovid, StMWK; grant to R.W. and K.Ü.) as well as by the National Research Network of the University Medicine (NUM; applied surveillance and testing; B-FAST) to K.Ü. and R.W. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.