In vitro neutralization titers against live WA1, Delta, BA.1, or BA.2 variants in unvaccinated (A and C) and vaccinated (B and D) hospitalized patients infected with a Delta (A and B) or Omicron (C and D) strain. Solid lines indicate sequence-confirmed infections; dashed lines, non-sequence-confirmed; red indicates immunocompromised patients. The ratio of BA.1- to WA1-neutralizing titers in unvaccinated (E) or vaccinated (F) patients. Geometric mean and 95% CI are indicated. For a subset of Omicron-infected patients who were unvaccinated (G) or vaccinated (H), BA.5 neutralization was also assessed. Values above the panels indicate fold differences between groups (P value). P values were calculated by Wilcoxon’s rank sum test.