This study compared SARS-CoV-2 sequences that were collected from infected patients (n=2,397) who were seen at NYU Langone Health facilities and globally (n=24,060 sequences in GISAID) between August 1, 2022, and February 4, 2023 to understand the proliferation of Omicron strain XBB.1.5. Active SARS-CoV-2 infection was confirmed with positive real-time (RT)-qPCR testing. To assess the association between patients' vaccination statuses, infection statuses, and detected strains, patients were categorized into the following groups:

1. Unvaccinated: Individuals who had not received a COVID-19 vaccine at the time of SARS-CoV-2 infection, and reported no prior SARS-CoV-2 infections.
2. Partially vaccinated: Individuals who contracted SARS-CoV-2 infection between the first vaccine shot and less than 14 days after completing their primary vaccination series.
3. Primary series: Individuals who completed their primary vaccination series at least 14 days ago. (I.e., after the second dose of BNT162b2 (Pfizer/BioNTech) or mRNA-1273 (Moderna) vaccines, or the single-dose COVID-19 Janssen vaccine.)
4. Boosted: Individuals who had received at least one additional COVID-19 shot (any vaccine) after completing the primary vaccination series.
5. Re-infected: Individuals who were infected with SARS-CoV-2 infection after having had a previous SARS-CoV-2 infection, regardless of their vaccination status and variant. This group included patients with multiple infections.

The viral genomes collected from patients at NYU Langone were also compared with 'background' SARS-CoV-2 sequences available in GISAID to estimate and compare the introduction and dispersal dynamics of the XBB.1.5 variant.