Postvaccination IgG and IgA antibodies in serum and breast milk samples of the study group (n = 28) compared to unvaccinated control group (n = 16): (a) Serum IgG—day 8 ± 1 (baseline) vs. no vaccination; Mann–Whitney p = 0.152; days 8 ± 1, 22 ± 2, 29 ± 3, and 43 ± 4; Friedman’s rank test p < 0.001 with post-hoc all pairwise comparisons p < 0.05. (b) Breast milk IgG—day 8 ± 1 (baseline) and no vaccination below detection limit; days 8 ± 1, 22 ± 2, 29 ± 3, and 43 ± 4; Friedman’s rank test p < 0.001 with post-hoc all pairwise comparisons p < 0.05. (c) Serum IgA—day 8 ± 1 (baseline) vs. no vaccination; Mann–Whitney p = 0.129; days 8 ± 1, 22 ± 2, 29 ± 3, and 43 ± 4; Friedman’s rank test p < 0.001 with post-hoc all pairwise comparisons p < 0.05. (d) Breast milk IgA—day 8 ± 1 (baseline) vs. no vaccination; Mann–Whitney p = 0.371; days 8 ± 1, 22 ± 2, 29 ± 3, and 43 ± 4; Friedman’s rank test p < 0.001 with post-hoc pairwise comparisons p < 0.05, except for no difference between days 22 ± 2 and 43 ± 4.