Table 2. Demographic, Clinical, and Laboratory Characteristics of Health Care Workers with Possible SARS-CoV-2 Reinfection.

Health Care Worker	Baseline Serologic Assay	No. of Days between Episodes*	Clinical Characteristics	Timing of PCR, Ct Value, and Assay	Follow-up Serologic Assay
Worker 1: White female physician, 25–29 yr of age	Anti-spike IgG: not detected Anti-nucleocapsid IgG: detected	160	1st episode: asymptomatic 2nd episode: symptomatic (mild, febrile illness)	1st episode: not done (before start of asymptomatic testing) 2nd episode: CN 10.6 (Abbott, assay), repeat extraction and PCR on same sample Ct 19.0 (Thermo Fisher assay)	Dual antibody seroconversion with a rise in anti-nucleocapsid IgG titer
Worker 2: White female nurse, 55–59 yr of age	Anti-spike IgG: detected Anti-nucleocapsid IgG: detected	190	1st episode: symptomatic (mild, Covid-19–like symptoms) 2nd episode: asymptomatic	1st episode: Ct 36.0 (PHE assay) 2nd episode: CN 21.2 (Abbott assay), repeat PCR on day 2 and day 4 both negative	No rise in antibody titers
Worker 3: White female administrator with patient contact, 50–54 yr of age	Anti-spike IgG: detected Anti-nucleocapsid IgG: not detected	199	1st episode: symptomatic (mild) 2nd episode: asymptomatic when tested (transient myalgia shortly after influenza vaccine 1 week earlier)	1st episode: PCR-negative 2nd episode: CN 12.6 (Abbott assay), repeat PCR on day 2 Ct 24.0 (Altona assay)	Dual antibody seroconversion, with a rise in anti-spike IgG titer

^*The number of days between episodes was calculated from the date of symptom onset if the index infection was symptomatic (as it was for health care Workers 2 and 3) or the date of the first clinic attendance if the presumed first episode was asymptomatic with no PCR performed (as it was for Worker 1). Both baseline serologic assays for Worker 1 were repeated and confirmed. A single positive PCR result for Worker 1 was confirmed by repeat nucleic acid extraction. Abbott PCR assay cycle number (CN) values are approximately equivalent to cycle threshold (Ct) values 10 units higher (e.g., CN 21 is approximately equivalent to Ct 31). See Figure S4 for quantitative antibody results. All PCR tests listed were performed at Oxford University Hospitals.