Study population

The cohort comprised 29 participants (14 females and 15 males) as previously described [3] with an average age of 44±13.2 years. All but one asymptomatic case had symptomatic COVID-19 with mild to moderate disease course and full recovery except for one person with persistent dysosmia.

All cases occurred in March and April 2020 and had a positive SARS-CoV‑2 antibody test in April 2020 at the latest. As defined by the original prospective study protocol, blood samples were serially collected at 4 time points after symptom onset, T1 between 2 weeks up to 2 months, T2 between 3 and 4 months, T3 at 6 months, and T4 at 12 months. Binding SARS-CoV‑2 antibodies were determined at all time points and neutralizing antibodies against the wild type (Wuhan) were done in all samples at T3 and T4. Additionally, neutralizing antibodies against the variants B.1.1.7 (alpha) and B.1.351 (beta) were tested at T4.

In three of five study participants who received COVID-19 vaccines coincidentally (and therefore constitutes a post hoc secondary endpoint) shortly before the last follow-up, samples were drawn immediately before vaccination and in 2 participants T3 was the last follow-up before vaccination. Therefore, the latter two persons were excluded from the T4 analysis for antibody persistency after infection. We also analyzed the change of antibody response in the five participants before and after vaccination including neutralization of the variants B.1.1.7 (alpha) and B.1.351 (beta).