Table 2.
Summarized definition and size of the groups used to classify donors for each assay
| Infection group | Definition | Number of donors | ||
|---|---|---|---|---|
| Assay-specific classification (anti-N) | Assay-specific classification (anti-S) | Final classification | ||
| Persistently seronegative | No positive results | 72 | 62 | 64 |
| Infection by non-Gamma variant | A positive result before Nov 1st 2020 and decaying antibody levels in 2021 | 100 | 81 | 90 |
| Infection by Gamma | No positive results in 2020 and a positive result in 2021 | 49 | 47 | 51 |
| Reinfection by Gamma | A positive result in 2021 and before Nov 1st 2020 and an intermediate result with value below these two readings (V-shaped S/C time series) | 9 | 22 | 8 |
| A positive result in 2021 succeeding two consecutive rising positive results in 2020 Donors in this group have an observed seroconversion period much longer than expected | 1 | 2 | 0 | |
| Probable reinfection by Gamma | One positive result in 2020 and a higher positive result in 2021 separated by an interval of at least (seroconversion period longer than expected) | 7 | 9 | 7 |
| Possible reinfection by Gamma | Classification as “Reinfection by Gamma” by only one assay (reinfection detected by one assay but not both) | 18 | ||
| Unknown (anti-S assay only) | Not enough volume to retest the sample with the anti-S assay | 15 | ||
| Total | . | 238 | 238 | 238 |
The final classification was obtained by combining the groups assigned by both assays according to Table 1. The definitions of probable reinfections depend on the parameter days for the anti-N assay and 126 days for the anti-S assay