SARS-CoV-2 and Its Variants in Thrice-Infected Health Workers: A Case Series from an Italian University Hospital.

Background: We described a SARS-CoV-2 thrice-infected case series in health workers (HW) to evaluate patient and virus variants and lineages and collect information on variables associated with multiple infections.

Methods: A retrospective analysis of clinical and laboratory characteristics of SARS-CoV-2 thrice-infected individuals was carried out in Verona University Hospital, concurrent with the ORCHESTRA project. Variant analysis was conducted on a subset of available specimens.

Results: Twelve HW out of 7368 were thrice infected (0.16%). Symptomatic infections were reported in 63.6%, 54.5% and 72.7% of the first, second and third infections, respectively. Nine subjects were fully vaccinated at the time of the third infection, and five had an additional booster dose. The mean time to second infection was 349.6 days (95% CI, 138-443); the mean interval between the second and third infection was 223.5 days (95% CI, 108-530) ( = 0.032). In three cases, the second and third infections were caused by the Omicron variant, but different lineages were detected when the second vs third infections were sequenced.

Conclusions: This case series confirms evidence of multiple reinfections with SARS-CoV-2, even from the same variant, in vaccinated HW. These results reinforce the need for continued infection-specific prevention measures in previously infected and reinfected HW.