Seroprevalence of Anti-SARS-CoV-2 IgG Antibodies in Tyrol, Austria: Updated Analysis Involving 22,607 Blood Donors Covering the Period October 2021 to April 2022

Abstract

Because a large proportion of the Austrian population has been infected with SARS-CoV-2 during high incidence periods in winter 2021/2022, up-to-date estimates of seroprevalence of anti-SARS-CoV-2 antibodies are required to inform upcoming public health policies. We quantified anti-Spike IgG antibody levels in 22,607 individuals that donated blood between October 2021 and April 2022 across Tyrol, Austria (participation rate: 96.0%). Median age of participants was 45.3 years (IQR: 30.9–55.1); 41.9% were female. From October 2021 to April 2022, seropositivity increased from 84.9% (95% CI: 83.8–86.0%) to 95.8% (94.9–96.4%), and the geometric mean anti-Spike IgG levels among seropositive participants increased from 283 (95% CI: 271–296) to 1437 (1360–1518) BAU/mL. The percentages of participants in categories with undetectable levels and detectable levels at <500, 500–<1000, 1000–<2000, 2000–<3000, and ≥3000 BAU/mL were 15%, 54%, 15%, 10%, 3%, and 3% in October 2021 vs. 4%, 18%, 17%, 18%, 11%, and 32% in April 2022. Of 2711 participants that had repeat measurements taken a median 4.2 months apart, 61.8% moved to a higher, 13.9% to a lower, and 24.4% remained in the same category. Among seropositive participants, antibody levels were 16.8-fold in vaccinated individuals compared to unvaccinated individuals (95% CI: 14.2–19.9; p-value < 0.001). In conclusion, anti-SARS-CoV-2 seroprevalence in terms of seropositivity and average antibody levels has increased markedly during the winter 2021/2022 SARS-CoV-2 waves in Tyrol, Austria.

Immune and behavioral correlates of protection against symptomatic post-vaccination SARS-CoV-2 infection

“…The finding that both anti-S bAb and NTs correlate strongly with protection against SARS-CoV-2 infection is consistent with a number of studies that have evaluated this issue previously 2,4,5,8,11–17 . Interestingly, even though NTs are often the principal biomarkers used to inform policy recommendations on booster doses 30,31 , our findings suggest that bAb levels may have similar utility for this purpose.…”

Single-Center Experience in Detecting Influenza Virus, RSV and SARS-CoV-2 at the Emergency Department

“…The early COVID-19 pandemic has thus hit a fully susceptible general population, and the first SARS-CoV-2 vaccines did not become available in Tyrol before January 2021. Therefore, there was little immunity against SARS-CoV-2 in March 2020, as evident from the 1.1–3.1% seroprevalence of SARS-CoV-2 in Austria between April and June 2020 [ 94 , 95 , 96 , 97 , 98 ], possibly delaying the effects of containment measures alone on SARS-CoV-2 transmission.…”

Cohort profile: a longitudinal regional cohort study to assess COVID-19 seroprevalence in blood donors – baseline characteristics of the SeMaCo study participants

“…Seropositivity there increased from 84.9% in October 2021 to 95.8% in April 2022, taking into account a very high vaccination coverage rate of 99.7% among seropositive participants. 33 …”

“…32 In Tyrolean blood donors with a similar age and sex distribution as in the SeMaCo study (43.65 years vs 45.3 years, female 48.2% vs female 41.9%), a significantly higher seroprevalence of SARS-CoV-2 antibodies was found in a later survey period than in the baseline study presented here, which were collected at an earlier point in the pandemic. Seropositivity there 33 The SeMaCo cohort has higher levels of education (CASMIN), which may have an impact on seroprevalence over the course of the study, as socioeconomically disadvantaged individuals have a higher risk of infection as well as a higher risk of a more severe clinical course of COVID-19. 34 For example, the likelihood of SARS-CoV-2 infection (seropositive/PCR-positive or previously tested positive) among participants with low education (classified by CASMIN) was higher in the cohort of the Nationwide Corona Monitoring study (RKI-SOEP) than in the group with high education (OR 1.87).…”

“…In Tyrolean blood donors with a similar age and sex distribution as in the SeMaCo study (43.65 years vs 45.3 years, female 48.2% vs female 41.9%), a significantly higher seroprevalence of SARS-CoV-2 antibodies was found in a later survey period than in the baseline study presented here, which were collected at an earlier point in the pandemic. Seropositivity there increased from 84.9% in October 2021 to 95.8% in April 2022, taking into account a very high vaccination coverage rate of 99.7% among seropositive participants 33…”