Efficient transplacental transfer of SARS-CoV-2 antibodies between naturally exposed mothers and infants in Accra, Ghana

Abstract

We aimed to determine SARS-CoV-2 antibody seropositivity among pregnant women and the transplacental transfer efficiency of SARS-CoV-2-specific antibodies relative to malaria antibodies among SARS-CoV-2 seropositive mother-cord pairs. This cross-sectional study was conducted in Accra, Ghana, from March to May 2022. Antigen- specific IgG antibodies against SARS-CoV-2 (nucleoprotein and spike-receptor binding domain) and malarial antigens (circumsporozoite protein and merozoite surface protein 3) in maternal and cord plasma were measured by ELISA. Plasma from both vaccinated and unvaccinated pregnant women were tested for neutralizing antibodies using commercial kit. Of the unvaccinated pregnant women tested, 58.12% at antenatal clinics and 55.56% at the delivery wards were seropositive for both SARS-CoV-2 nucleoprotein and RBD antibodies. Anti-SARS-CoV-2 antibodies in cord samples correlated with maternal antibody levels (N antigen r_s = 0.7155, p < 0.001; RBD r_s = 0.8693, p < 0.001). Transplacental transfer of SARS-CoV-2 nucleoprotein antibodies was comparable to circumsporozoite protein antibodies (p = 0.9999) but both were higher than transfer rates of merozoite surface protein 3 antibodies (p < 0.001). SARS-CoV-2 IgG seropositivity among pregnant women in Accra is high with a boost of SARS-CoV-2 RBD-specific IgG in vaccinated women. Transplacental transfer of anti-SARS-CoV-2 and malarial antibodies was efficient, supporting vaccination of mothers as a strategy to protect infants against SARS-CoV-2.

Keywords: COVID-19; Maternal COVID-19; Prenatal COVID-19 placental transfer; SARS-COV-2; Transfer efficiency.

Figure 1

Seroprevalence to SARS-CoV-2 is high in pregnant women. IgG antibody seropositivity of SARS-COV-2 N-antigen (a) and RBD antigen (b) in plasma from pregnant women at antenatal and delivery wards. Seropositivity against N antigen alone (blue), RBD alone (green) and both antigens (grey).

Figure 2

Placental transfer of IgG between seropositive mothers to matching cord. SARS-CoV-2 antibodies against nucleoprotein (N) protein (A) and RBD (B) between mother:cord pairs. Spaghetti lines represent antibody levels between mother and matching cord sample. Box and whisker represent median with interquartile range. Correlation between maternal and cord IgG antibody levels against nucleoprotein (C) and RBD (D) presented in linear regression. Shaded are depicts 95% confidence interval. r represents the spearman’s rank coefficient .

Figure 3

Transfer efficiency of SARS-CoV-2 and malaria-specific antibodies. Cord:maternal antibody transfer ratio of antigens among SARS-CoV-2 seropositive individuals (a). Transfer ratio of CSP (b) and MSP3 (c) among SARS-CoV-2 seropositive paired mother:cord plasma samples and pre-pandemic paired mother:cord plasma samples. Transfer ratio was calculated as: (cord IgG concentration)/(maternal IgG concentration). Kruskal Wallis test was used to analyse comparisons in A. Mann–Whitney test was used to compare transfer ratios in b and c. Data is presented as geometric mean (thick horizontal lines) and 95% confidence interval (error bars).

Figure 4

Inhibition of ACE2 binding in SARS-CoV-2 seropositive pregnant. Percentage binding inhibition between seropositive pregnant women at antenatal clinics and at delivery (a). Inhibitory antibodies transferred from mothers to cord (b). Bars indicate median binding inhibition. Horizontal dashed lines represent 50% inhibition.

Figure 5

Vaccination against SARS-CoV-2 causes a boost in spike-RBD specific antibodies. Antibody levels against N antigen (a) and Spike-RBD (b) between pregnant women vaccinated against COVID-19 and unvaccinated pregnant women. ACE-2 binding inhibition rates between pregnant women vaccinated against COVID-19 and unvaccinated pregnant women (c). Mann–Whitney test was used to analyse comparisons between groups.