Persistence of immunity to SARS-CoV-2 over time in the ski resort Ischgl

Abstract

Background In early March 2020, a SARS-CoV-2 outbreak in the ski resort Ischgl in Austria triggered the spread of SARS-CoV-2 throughout Austria and Northern Europe. In a previous study, we found that the seroprevalence in the adult population of Ischgl had reached 45% by the end of April, representing an exceptionally high level of local seropositivity in Europe. We performed a follow-up study in Ischgl, which is the first to show persistence of immunity and protection against SARS-CoV-2 and some of its variants at a community level. Methods Of the 1259 adults that participated in the baseline study, 801 have been included in the follow-up in November 2020. The study involved the analysis of binding and neutralizing antibodies and T cell responses. In addition, the incidence of SARS-CoV-2 and its variants in Ischgl was compared to the incidence in similar municipalities in Tyrol until April 2021. Findings For the 801 individuals that participated in both studies, the seroprevalence declined from 51.4% (95% confidence interval (CI) 47.9–54.9) to 45.4% (95% CI 42.0–49.0). Median antibody concentrations dropped considerably (5.345, 95% CI 4.833 – 6.123 to 2.298, 95% CI 2.141 – 2.527) but antibody avidity increased (17.02, 95% CI 16.49 – 17.94 to 42.46, 95% CI 41.06 – 46.26). Only one person had lost detectable antibodies and T cell responses. In parallel to this persistent immunity, we observed that Ischgl was relatively spared, compared to similar municipalities, from the prominent second COVID-19 wave that hit Austria in November 2020. In addition, we used sequencing data to show that the local immunity acquired from wild-type infections also helped to curb infections from variants of SARS-CoV-2 which spread in Austria since January 2021. Interpretation The relatively high level of seroprevalence (40–45%) in Ischgl persisted and might have been associated with the observed protection of Ischgl residents against virus infection during the second COVID-19 wave as well as against variant spread in 2021. Funding Funding was provided by the government of Tyrol and the FWF Austrian Science Fund.

Prevalence of SARS-CoV-2 antibodies in healthy blood donors from the state of Tyrol, Austria, in summer 2020

“…Our study is the first to quantify seroprevalence of SARS-CoV‑2 antibodies in the whole federal state of Tyrol, Austria, estimating it at 3.1%. A previous study conducted among 1473 inhabitants of the Austrian ski resort Ischgl has shown a seroprevalence of 42.4% in the end of April 2020 [ 3 ] and an absolute reduction of 6.7% among 801 individuals with a repeat measurement after a 6-month follow-up [ 14 ]. In line, we also show a higher seroprevalence of 16.6% in the whole district of Landeck and 33.0% among blood donors living in Ischgl, whereas seroprevalence in other districts of Tyrol was substantially lower.…”

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

“…The primary analysis quantified the seroprevalence of anti-SARS-CoV-2 IgG antibodies for each of the months between June 2020 and September 2021; it is here presented together with Agresti–Coull 95% CIs. Serological tests in August and September 2020 were excluded because they were considered as non-representative samples (e.g., 71.4% in Ischgl [ 12 ]). Because the offer to test for anti-SARS-CoV-2 IgG antibodies as part of a blood donation may have mobilized individuals and may thereby have introduced some selection bias, we conducted a sensitivity analysis restricted to individuals with repeat donations since October 2017.…”

12-month SARS-CoV-2 antibody persistency in a Tyrolean COVID-19 cohort

“…Even early after disease only 74% of patients had levels above threshold for positivity, possibly indicating a sensitivity issue of this particular test system. This must be considered when using this assay for confirmation of possible infection after vaccination as such a strong decay did not occur using other systems [ 11 ].…”

“…Titers of neutralizing antibodies against SARS-CoV‑2 Wuhan strain were determined using vesicular stomatitis virus (VSV)-based assay and titers against SARS-CoV‑2 variants using a focus forming assay with replication competent SARS-CoV‑2 as previously described [ 11 ]. Briefly, for the VSV pseudovirus assay 4‑fold dilutions of heat-inactivated serum samples were incubated with a replication defective VSV expressing green fluorescent protein (GFP) as marker gene and pseudotyped with a C-terminally truncated version of the spike protein of SARS-CoV‑2 (Wuhan isolate) for 1 h. Consequently, 293T stably overexpressing human angiotensine converting enzyme (ACE)2 receptor, were infected with pseudovirus.…”