Figure 4.

HCWs salivary IgA levels

(A) Detection of salivary IgA levels in 81 HCWs who previously had COVID-19, 34 vaccinated HCWs, and 33 HCWs with breakthrough infections measured at different time points after the first positive NPS (0–3 days, 4–6 days, 7–10 days, 11–14 days, >15 days, and 5–8 months). Empty circles refer to HCWs for which only one sample was collected at a known time point after the first positive NPS (n = 19). Statistical significances are reported in the table besides the graph. Medians are indicated, and statistical significance was determined using unpaired Mann-Whitney t test. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001; ^∗∗∗∗p < 0.0001. (B) Graphical model of the possible mechanism by which SARS-CoV-2 infection turns vaccine-induced systemic immunity into local immunity. In vaccinated individuals, specific antibodies reach mucosal sites by transudation (on the left). After infection, memory T and B cells reach the site of viral entry. MBCs differentiate into plasma cells secreting large amounts of specific IgA (on the right).