Table 2.
Seroprevalence estimatesa (IgG anti Sars-CoV-2 Spike) by study period and canton, Corona Immunitas study, Switzerland, May 2020–September 2021
| Time window | Period 1, n = 3402 | Period 2, n = 5611 | Period 3, n = 4278 |
|---|---|---|---|
| 01/05/2020–31/10/2020 | 01/11/2020–15/05/2021 | 16/05/2021–31/09/2021 | |
| % (95%CI) | % (95%CI) | % (95%CI) | |
| National level | 3.7 (2.1–4.9) | 16.2 (14.4–17.5) | 72.0 (70.3–73.8) |
| Basel-Landschaft | 2.9 (1.3–5.4) | 16.5 (13.4–19.9) | 82.8 (78.0–87.3) |
| Basel-Stadt | 5.0 (2.6–7.8) | 19.7 (16.2–23.2) | 77.2 (72.7–81.6) |
| Bern | NA | 10.9 (7.4–14.7) | 78.1 (74.1–82.0) |
| Fribourg | 5.9 (3.2–9.1) | 22.5 (18.7–26.6) | 73.5 (68.4–78.4) |
| Grisonsb | NA | 15.7 (11.5–20.3) | 43.2 (37.2–49.3) |
| Lucerne | NA | 15.5 (11.7–19.7) | 58.9 (54.4–63.6) |
| Neuchâtel | 3.0 (1.4–5.4) | 19.2 (15.4–23.1) | 79.2 (74.8–83.2) |
| Saint Gallenb | NA | 11.7 (7.8–16.5) | 62.2 (56.6–68.0) |
| Ticinoc | 7.7 (5.3–10.3) | 6.8 (4.1–9.7) | NA |
| Vaud | 6.5 (3.8–9.8) | 23.7 (20.3–27.1) | NA |
| Zurich | 2.1 (1.0–3.6) | 9.7 (6.7–13.0) | 78.5 (74.3–82.5) |
Samplings in Bern, Grisons, Lucerne and Saint Gallen started after period 1. Data for Ticino and Vaud period 3 were not available for the analyses presented in this study
IgG immunoglobulin G, NA not available
aSeroprevalence was estimated using Bayesian regression adjusted for the antibody test sensitivity and specificity performances and weighted by age and sex of the general population of each canton
bIn cantons Grisons and Saint Gallen, only participants aged from 20 to 64 years were tested
cIn canton Ticino, during period 1, only participants aged from 20 to 64 were tested. During period 2 only data from people aged 65 years or more were available for these analyses