Pregnancy reduces COVID-19 vaccine immunity against novel variants

Abstract

Pregnant women are at heightened risk for severe outcomes from infectious diseases like COVID-19, yet were not included in initial vaccine trials, which may contribute to low booster uptake (15% or lower). We explored the serological and cellular responses to COVID-19 mRNA booster vaccines (i.e., ancestral and BA.5) in pregnant and age-matched, non-pregnant females to identify how pregnancy affects immunity against the vaccine and novel variants. Antibodies from pregnant women were less cross-reactive to non-vaccine antigens, including XBB.1.5 and JN.1. Non-pregnant females showed greater IgG1:IgG3 ratios and neutralization against all variants. In contrast, pregnant women had lower IgG1:IgG3 ratios and neutralization but increased antibody-dependent NK cell cytokine production and neutrophil phagocytosis, especially against novel variants. Pregnancy increased memory CD4+ T cells, IFNγ production, monofunctional dominance, and fatty acid oxidation. Pregnancy may reduce the breadth, composition, and magnitude of humoral and cellular immunity, particularly in response to novel variants.

Fig. 1. Vaccination differently induces IgG subtype responses during pregnancy.

IgG antibody responses in serum pre- and 3–5 weeks post-vaccination were measured by systems serology and reported as log₁₀ mean fluorescence intensity. Pregnant women (n = 7) are shown in orange and non-pregnant females (n = 13) in purple. Triangles highlight women who received monovalent boosters, and circles represent bivalent booster recipients. Horizontal bars indicate mean MFI across samples, with bars indicating standard error of the mean. A Total IgG to ancestral nucleocapsid (N) protein. B Total IgG separated by SARS-CoV-2 vaccine (ancestral and BA.5) and variant (XBB1.5 and JN.1) spike (S) antigen and pregnancy status. Relative abundance of IgG subtypes in pregnant and non-pregnant women as stacked bar plots representing each isotype as a percentage of total IgG by (C) ancestral S, (D) BA.5 S, (E) XBB.1.5 S, and (F) JN.1 S. Data were analyzed by A repeated measures two-way ANOVA B linear mixed effects regression analysis with Bonferroni post-hoc. C–F Isotype proportions were analyzed by Chi-squared analysis, with values reported under each corresponding graph. Asterisks indicate p < 0.05. The stippled line indicates the limit of background (LOB), defined as the log₁₀MFI of a defined negative control.

Fig. 2. Pregnancy alters cross-neutralization of variants of concern.

IgG antibody responses in serum pre- and 3–5 weeks post-vaccination were measured by systems serology and reported as mean fluorescence intensity. Pregnant women (n = 7) are shown in orange and non-pregnant females (n = 13) in purple. Triangles highlight women who received monovalent boosters, and circles represent bivalent booster recipients. Bars represent mean MFI across samples, with bars indicating standard error of the mean. A–E Ratio of IgG1:IgG3 antibodies specific to A ancestral spike (S), B BA.5 S, C XBB.1.5 S, and D JN.1 S. Neutralizing antibody titers reported as Log₂ NT50 against E ancestral, F BA.5, G XBB.1.5, and H JN.1 viruses. Ratios shown on the x-axis indicate the number of women per group/timepoint that are above the limit of detection (LOD) indicated by the stippled line. Pearson correlations between IgG1:IgG3 ratios and neutralizing antibody titers reported as Log₂ NT50 to I ancestral spike (S), J BA.5 S, K XBB.1.5 S, and L JN.1 S. A–H Data were analyzed by repeated measures two-way ANOVA with Bonferroni post-hoc. Asterisks indicate p < 0.05. I–L Regression lines for each group are shown in dashed lines colored according to cohort. Separate R² and p values are shown for each variant, separated by pregnancy status.

Fig. 3. Fc receptor binding is reduced in pregnant women in response to variants of concern.

Serum antibody Fc receptor (FcR) binding pre- and 3–5 weeks post-vaccination was measured by multiplex Luminex-bead assays and reported as log₁₀ mean fluorescence intensity. Pregnant women (n = 7) are shown in orange and non-pregnant females (n = 13) in purple. Triangles highlight women who received monovalent boosters, and circles represent bivalent booster recipients. Horizontal bars indicate mean MFI across samples, with bars indicating standard error of the mean. Antibody binding to FcγRIIA-R, FcγRIIA-H, FcγRIIb, FcγRIIIA-V, FcγRIIIA-F, FcγRIIIB, FcRn, and FcαR was determined for A ancestral spike (S), B BA.5 S, C XBB.1.5 S, and D JN.1 S. Data were analyzed by linear mixed effects regression analysis with Bonferroni post-hoc. Asterisks indicate p < 0.05. The stippled line indicates the limit of background (LOB), defined as the log₁₀MFI of a defined negative control.

Fig. 4. Non-neutralizing and neutralizing antibody functions are negatively correlated among pregnant women.

Non-neutralizing antibody functions were measured pre- and 3–5 weeks post-vaccination. Pregnant women (n = 7) are shown in orange and non-pregnant females (n = 13) in purple. Triangles highlight women who received monovalent boosters, and circles represent bivalent booster recipients. Horizontal bars indicate mean MFI across samples, with bars indicating standard error of the mean. A Antibody-dependent complement deposition (ADCD) was measured by assessing antibody binding to C3 protein and is reported as log₁₀ mean fluorescence intensity. The stippled line indicates the limit of background (LOB), defined as the log₁₀MFI of a defined negative control. NK cells isolated from donor blood were utilized to assess B antibody-dependent NK-cell cytotoxicity (ADNK), or the ability of antigen-specific serum antibody to induce NK-cell cytokine production or degranulation. Data are reported as % MIP1B+ cells of CD16+/CD56+ NK cells. C THP-1 monocyte cell line was used to measure antibody-dependent cellular phagocytosis (ADCP), or the ability of antibody to induce phagocytosis of an antigen. D Neutrophils isolated from donor blood were used to measure antibody-dependent neutrophil phagocytosis (ADNP), or the ability of antibody to induce neutrophil phagocytosis of an antigen. ADCP and ADNP are reported as a PhagoScore, calculated as (% bead-positive monocytes/neutrophils) × (geometric MFI of each cell). Pearson correlations between post-vaccination neutralizing antibody titers (Log₂ NT50) and ADNP PhagoScores are shown for: E ancestral, F BA.5, G XBB.1.5, and H JN.1 viruses. A–E Data were analyzed by linear mixed effects regression analysis with Bonferroni post-hoc with asterisks indicating p < 0.05. E–H Separate Pearson correlation R² and p values are shown for each variant, separated by pregnancy status, with p < 0.05 shown in bolded font. Regression lines for each group are shown in dashed lines colored according to cohort.

Fig. 5. Correlations among IgG subclasses and antibody functional phenotypes differ between pregnant and non-pregnant women.

A Pre-vaccination and B post-vaccination systems serology measures, including isotype subclasses, FcR binding, non-neutralizing functions, and neutralizing antibody titers, were log₁₀ transformed and used for Spearman correlation analyses. Isotypes (y-axis) were correlated with functional measures (x-axis). Analyses were performed by pregnancy status. Asterisks indicate p < 0.05. Colors indicate Spearman correlation R value with a positive correlation of 1 indicated by deep red and a negative correlation of 1 indicated by deep blue. ADNP antibody-dependent neutrophil phagocytosis, ADCP antibody-dependent cellular phagocytosis, ADNK antibody-dependent NK-cell cytotoxicity, ADCD antibody-dependent complement deposition, NT neutralizing antibody titer.

Fig. 6. CD4+ T cells have reduced polyfunctionality among pregnant women.

Peripheral blood mononuclear cells (PBMCs) were collected pre- and 3–5 weeks post-vaccination for flow-cytometry analyses. Cytokine-producing, antigen-specific CD4⁺ T cells for A pregnant (n = 7) and B non-pregnant (n = 3) women are represented in pie charts broken down by the 15 cytokine combination categories. Arcs identify portions of the pie that express each specific cytokine. Paired dot plots demonstrate the percentage of memory CD4⁺ T cells producing C IFNγ, D TNF, E IL-2, or F IL-21 following stimulation with ancestral SARS-CoV-2 spike peptide pools pre- and post-vaccination. Data were analyzed by linear mixed effects regression analysis with Bonferroni post-hoc. Asterisks indicate p < 0.05.

Fig. 7. Carnitine palmitoyl transferase 1A (CPT1a) expression in CD4+ and CD8+ T cells pre- and post-vaccination is higher in pregnant women.

Peripheral blood mononuclear cells (PBMCs) were collected pre- and 3–5 weeks post-vaccination for flow-cytometry analyses. Histograms showing CPT1a expression in total A CD4⁺ and C CD8⁺ T cells from peripheral blood mononuclear cells collected pre- and 3–5 weeks post-vaccination. Pregnant individuals (n = 7) are shown in orange and non-pregnant individuals (n = 3) in purple. Quantification of mean fluorescence intensity in memory CD4⁺ (B) and memory CD8+ (D) T cells is shown for each group pre- and post-vaccination. Horizontal bars indicate mean MFI across samples, with bars indicating standard error of the mean. Data were analyzed by linear mixed effects regression analysis with Bonferroni post-hoc. Asterisks indicate p < 0.05.