Figure 2.

Induction of cross-neutralizing antibodies at the nasal mucosae upon Omicron BA.1 or BA.2 breakthrough infection

Nasal swabs were collected at 1 month after the third dose for 20 participants (median = 38 days after the third dose) and 1–3 months after BA.1 or BA.2 breakthrough infection for 7 participants. In 5 participants who experienced a breakthrough infection, 2 or 3 time points after infection are shown, representing a total of 15 samples.

(A) Levels of anti-spike IgGs (left panel) and IgAs (right panel) measured by flow cytometry with the S-Flow assay. For IgGs, results are presented in BAU/mL. The dotted lines indicate the limit of detection (3 BAU/mL). For IgAs, the mean fluorescence intensity of binding is shown, since the lack of IgA reference samples precluded a calculation of BAU IgA/mL. Black lines represent the median values. A Mann-Whitney unpaired t-test was performed. ∗∗∗∗p < 0.0001.

(B) The Nab titers against D614G, Delta and Omicron BA.1, BA.2, and BA.5 were measured in the same samples from triple vaccinated individuals (left panel) and after breakthrough infection (right panel). The dotted lines indicate the limit of detection (ED₅₀ = 4). Black lines represent the median values. A two-sided Friedman test with Dunn’s test for multiple comparisons was performed between each viral strain at the different time points; ∗∗p < 0.01.