Figure 2.

Neutralizing antibodies are found in blood and less frequently in milk after second vaccine dose

(A) Anti-spike IgG, IgA, and IgM at ∼10 days after first (prime) and second (boost) vaccine doses in plasma and in skim milk, measured by absorbance at 450 nm (OD₄₅₀).

(B) Anti-RBD IgG, IgA, and IgM performed as in (A).

(C) Correlation between anti-spike IgA in skim milk versus anti-spike IgG in the blood.

(D) Comparison between anti-spike- and anti-RBD SIgA at ∼10 days after first (prime) and second (boost) vaccine doses, measured as in (A).

(E) Donor-matched analysis of anti-spike IgG, IgA, and SIgA, pre-vaccination and after first (prime) and second (boost) vaccine doses, in skim milk.

(F) Donor-matched analysis of anti-spike IgG, IgA, and IgM, pre-vaccination and after first (prime) and second (boost) vaccine doses, in blood.

(G) Plasma neutralization curves.

(H) Plasma neutralization titers (NT₅₀) in nursing and control women.

(I) Skim milk neutralization curves.

(J) Neutralization curves for skim milk purified IgA concentrated 5-fold, pre-vaccination and ∼10 days after vaccine boost.

(K) Neutralization curves for skim milk purified IgG concentrated 5-fold, pre-vaccination and ∼10 days after vaccine boost.

Orange, plasma; purple, skim milk. Circles, Pfizer; squares, Moderna. Dashed line, assay cutoff. n = 23 nursing women and n = 22 controls. p values determined using parametric paired t test and non-parametric paired Wilcoxon test as appropriate and using ANOVA, post hoc Holm-Sidak and Kruskal-Wallis tests, and post hoc Dunn test when comparing three groups. Spearman correlation. ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001, and ∗∗∗∗p < 0.0001; ns, not significant.