Maternal and neonatal SARS‐CoV‐2 antibodies assessment after mRNA maternal vaccination in the third trimester of pregnancy

Synopsis

Vaccine immunization against SARS‐Cov‐2 is transferred to the fetus; however, transplacental passage of antibodies after vaccination might be less efficient than in natural infection.

Transplacental passage of antibodies is a key element of neonatal immunity. Data from the existing literature show that maternal immunoglobulin G (IgG) antibodies, produced in response to SARS‐CoV‐2, are transferred across the placenta after both asymptomatic and symptomatic COVID‐19 infection during pregnancy. ¹

SARS‐CoV‐2 vaccination was initially considered to be contraindicated in pregnant populations due to the lack of safety data; however, many scientific associations expressed their favor for vaccination in pregnancy after an accurate evaluation of the personal risk/benefit ratio. At present, the American College of Obstetricians and Gynecologists (ACOG) recommends SARS‐CoV‐2 vaccination for pregnant women, which is similar to their stance on other high risk medical conditions and the recommendations outlined by the Center for Disease Control and Prevention (CDC). ²

The present study reports the case of a healthy 42‐year‐old pregnant healthcare worker who received a Comirnaty (Pfizer/BioNTech SE.) mRNA vaccination at 31 and 34 weeks of gestation. Written informed consent was obtained from the patient for the publication of this study. Ethics Committee approval was not needed for this study.

Previously, the patient tested negative for SARS‐CoV‐2 antibodies, and rhinopharingeal swab for SARS‐CoV‐2 was negative at admission. At 39 weeks of gestation, the patient gave birth to a healthy baby girl by cesarean delivery, weighing 3030 g. Maternal blood was tested for SARS‐CoV‐2 IgG spike protein antibody the day before delivery by electrochemiluminescence immunoassay and the results indicated 62 U/ml (positive >20 U/ml). A cord blood sample was taken at birth and yielded a result of 25 U/ml. In the literature, similar findings were reported for Moderna (Moderna Inc.) mRNA vaccination in a woman who received a single dose 3 weeks before delivery. ³ A recent study on 20 women with previous SARS‐CoV‐2 infection showed that transplacental passage of antibodies against the virus is directly correlated with maternal viral load and inversely correlated with the infection‐to‐delivery interval. ⁴  The mean ratio between cord and maternal antibodies at birth was 1.3 (0.9–1.6). ⁴  This result is similar to a previous paper, that reported a placental ratio of more than 1.0 in 40 out of 72 neonates who tested positive for SARS‐CoV‐2 IgG antibodies after maternal infection. ¹

In our case, the ratio between cord and maternal antibodies was 0.38. This may imply that transplacental passage of antibodies after vaccination might be less efficient than in natural infection. If confirmed, this could have important implications for future vaccine designs for pregnant populations (e.g., regarding the best timing of an eventual recall). Nevertheless, further protections to ensure that neonates are not infected by their mothers and their closest contacts are needed. For this reason, we believe that pregnant populations should be vaccinated too (I.e., the “cocoon strategy”, as similarly used for pertussis vaccination).

CONFLICTS OF INTEREST

The authors have no conflict of interest.

AUTHOR CONTRIBUTIONS

CR contributed to the study conception and analysis of data, drafting, and approval of the manuscript. VP was responsible for the review of the literature and drafting of the manuscript. All authors contributed to and approved of the final version of the manuscript.