A Study of Transplacental Transfer of SARS-CoV-2 Antibodies in COVID-19 Vaccinated Women in Mumbai, India.

Background Antibodies generated in response to vaccination in mothers are efficiently transferred across the placenta. The transfer of these antibodies may depend on the time of vaccination during pregnancy, the type of vaccine, and the number of doses, including booster doses. We designed the present study to study the correlation between anti-spike (anti-S), anti-nucleocapsid (anti-N), and neutralizing antibodies in vaccinated mothers and neonates in Mumbai, India. We also wanted to evaluate the factors affecting the level of antibodies in mothers and neonates. Methods The present study is a cross-sectional analysis of 125 mother-neonate dyads in Mumbai, India. We recruited a consecutive consenting sample of mothers who were in the period of 37 to 42 weeks. We collected blood from the mothers just prior to delivery, and cord blood was used for testing in newborns. In addition, we also collected information on demographics, pregnancy, COVID-19 history, and vaccination details. We performed tests for three types of antibodies in these two types of blood samples for each dyad: anti-S, anti-N, and neutralizing antibodies. Results The mean (SD) age of the women was 28.8 (3.5) years. Most of them were at 37 weeks of gestation (56%), and 44% were at 38 or 39 weeks of gestation. All the women had taken two doses of the Covishield™ vaccine, and the mean (SD) duration between the second dose and date of delivery was 14.1 (1.4) months. The median (IQR) value of anti-S antibodies was 3012 (1555, 5000) U/ml in the mother, and it was 3749 (1636, 5000) U/ml in the cord blood. There was 100% reactivity to the anti-N antibodies in the mother and the cord blood (based on the cut-off index). There was 85.6% (n=107) positivity for neutralizing antibodies in the mother and 82.4% (n=103) positivity in the cord blood. The transfer ratio of > 1 was seen in 37.6% for anti-S antibodies and 51.2% for neutralizing antibodies; it was significantly higher for neutralizing antibodies compared with anti-S antibodies (p=0.03). In linear regression models, an increase of one unit of anti-S antibody in the mother was associated with an increase of 0.95 (95% confidence interval [CI]: 0.89, 1.00; p<0.001) U/ml in the baby. The positivity for these antibodies was significantly lower in the cord blood with an increase in the duration of the last dose of the vaccine in the mothers (odds ratio: 0.57, 95% CI: 0.34, 0.95; p=0.03). Conclusions We found that there was a significantly high positive correlation between the levels of COVID-19 antibodies in vaccinated mothers and the cord blood of neonates. Time since vaccination reduced the levels of antibodies in mothers; however, the drop per month was significant only for anti-S antibodies. The time of vaccination in the mothers was significantly associated with positivity for neutralizing antibodies in the cord blood; the positivity reduced with an increase in duration between the second vaccine and birth. There was no significant association between the age of the mother or gestation age and antibody levels in the cord blood.