Vaccinated mothers may pass on SARS-CoV-2 antibodies to newborns

Even as the ongoing pandemic of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to cause thousands of deaths and millions of infections worldwide, researchers are anxiously following the infection and mortality rates in vaccinated populations. This will help arrive at a preliminary estimate of vaccine efficacy in terms of containing the spread of the virus.

SARS-CoV-2 infection in pregnancy

One of the high-risk groups requiring special protection from SARS-CoV-2 infection is pregnant women. A burning question is whether vaccination of this category will elicit protective antibodies that are capable of transplacental passage, to the fetus or newborn. A new preprint released on the medRxiv* server describes the first case of anti-SARS-CoV-2 antibodies detected in the cord blood of an infant born to a mother immunized with the first dose of an mRNA COVID-19 vaccine three weeks earlier.

Earlier, the administration of influenza and TDaP (Tetanus, diphtheria and pertussis) vaccines to pregnant women has been associated with the presence of antibodies in the newborn, protecting the latter against these diseases, with a high level of safety and efficacy.

This has led to recommendations that pregnant women receive the influenza and TDaP vaccines during their period of gestation, in order to protect their newborn infants against these diseases. A similar effect was to be expected following maternal vaccination against COVID-19, but data are lacking to back such a recommendation.

Cord blood shows SARS-CoV-2 antibodies

The current study aims to contribute to the sum of evidence for protective neonatal immunity induced by maternal vaccination with current vaccines against SARS-CoV-2. The subject of the study is a front-line healthcare worker who received the first dose of the Moderna vaccine, an mRNA vaccine, while she was 36 weeks pregnant.

Three weeks later, she delivered a healthy baby girl by spontaneous vaginal birth. The infant was vigorous and normal to all appearances, and according to standard well-infant evaluation. The mother began exclusive breastfeeding and received the second vaccine dose at the right time, during her postpartum period.

Immediately after birth, cord blood sampling was performed under aseptic conditions. Along with the newborn blood typing and direct antiglobulin test (DAT), a sample was used to assay antibodies to the SARS-CoV-2 virus spike protein. The method used was the quantitative electrochemiluminescence Immunoassay (ECLIA).

The cord blood was demonstrated to contain immunoglobulin G (IgG) antibodies to the virus, at a level of 1.3 U/mL. These antibodies specifically targeted the receptor-binding domain (RBD) of the spike antigen.

What are the implications?

The investigators report this to be the first time maternally-derived cord blood antibodies to SARS-CoV-2 have been detected after the immunization of the mother with a COVID-19 vaccine.

In the light of earlier findings, it should be expected that the new mRNA vaccines against SARS-CoV-2 will lead to effective protection against the infection for newborns of immunized mothers. This needs to be established, however, by experimental evaluation, since natural infection with this virus is not, apparently, associated with the expected high level of transplacental passage of protective antibodies.

In the current study, detectable levels of IgG antibodies to the SARS-CoV-2 virus were found in the cord blood sample of a baby born to a mother who had received the first dose of the Moderna vaccine. This indicates that protection is potentially possible, as is a reduction in the risk of infection, for babies of vaccinated mothers.

The antibody response in cord blood needs to be quantified, say the researchers, by determining the titer of specific neutralizing antibodies in the infant’s blood.

Future directions

Again, future longitudinal studies will be required to explore variations in antibody titer over time with different patients. This will show how long protection may be expected to last following natural infection or vaccination.

This, in turn, will indicate the best time to begin immunization of pregnant women with an eye to optimal neonatal protection. Again, the ideal start point of immunization against COVID-19 in pregnancy, before delivery, needs to be evaluated to provide the baby with the highest titer of neutralizing antibodies after birth.

We urge other investigators to create pregnancy and breastfeeding registries as well as conduct efficacy and safety studies of the COVID-19 vaccines in pregnant and breastfeeding woman and their offspring.”

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.