Pregnant women who receive COVID-19 vaccine pass antibodies to newborns, study finds

Women who receive the mRNA novel coronavirus (COVID-19) vaccine during pregnancy pass high levels of antibodies to their babies, according to a new study published in the American Journal of Obstetrics & Gynecology—Maternal–Fetal Medicine.

The effectiveness of the Pfizer–BioNTech and Moderna mRNA COVID-19 vaccines, the researchers said, lies in their ability to trigger the production of the right antibodies, blood proteins capable of protecting individuals from infection. Whether this protection could pass from mothers to their infants before birth had remained a question.

For the study, which included 36 newborns whose mothers received either the Pfizer–BioNTech or Moderna COVID-19 vaccine during pregnancy, researchers found that 100 percent of the infants had protective antibodies at birth. The authors observed the highest levels of antibodies in cord blood of mothers who were fully vaccinated during the second half of their pregnancies. This insight provides evidence of transferred immunity to neonates, which correlates to protection against infection for infants during the first months of life.

Antibodies can either be produced as part of the natural response to infection or triggered by vaccines. With that in mind, the research team was able to tell apart antibodies in the neonatal blood that were created in response to natural infection from those made in response to the vaccines.

The result is relevant because natural antibody responses against the SARS-CoV-2 virus are not sufficiently protective for many people. Recent data from the U.S. Centers for Disease Control and Prevention (CDC) suggests that just 23 percent of pregnant women have been vaccinated, despite growing evidence of prenatal vaccine safety.

Existing studies analyze antibodies to the spike protein (anti-S IgG) alone, which may be present after natural infection or vaccination, and do not include antibodies to the nucleocapsid protein (anti-N IgG), which is only present following natural infection. Among the 36 samples collected, all had high levels of anti-S IgG. Of those samples, 31 were tested for anti-N IgG and were negative.

Additional research is needed to determine how effective the infant antibodies are, how long protection will last, and if vaccination in the second half of pregnancy may confer higher levels of antibody transfer than vaccination earlier in pregnancy. Future studies should also focus on antibody transmission to newborns in a larger population and durability of antibody detection during infancy.

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