Introduction
The global outbreak of severe acute respiratory syndrome coronavirus 2
(SARS-CoV-2) in December 2019 has been a worldwide concern. Taiwan,
being an isolated island in East Asia, had a low incidence of SARS-CoV-2
infection until 2020.(1, 2) In Taiwan, the pandemic surged in April 2022
with the Omicron variant (BA.2.3.7) being identified as the major
lineage.(3)
Pregnant individuals are encouraged to receive the SARS-CoV-2 vaccine
because of the higher risk of adverse outcomes, such as death,
intubation, admission to an intensive care unit, preterm birth,
preeclampsia, venous thromboembolism, and other severe
comorbidities.(4-6) The safety of SARS-CoV-2 vaccination during
pregnancy has been supported by current evidence.(7, 8)
Newborns have immature immune systems and are vulnerable to infectious
diseases. Neonatal passive immunity mainly depends on the maternal
concentration of respective antibodies for most viral diseases.(9) Low
or early disappearance of maternal-derived antibody concentrations can
lead to insufficient protection for newborns. Maternal-derived,
vertically transferred immunity provides protection for newborns against
vaccine-preventable infectious diseases, such as measles, mumps, and
rubella, which cannot be administered to infants before 12 months.(10)
Similarly, no SARS-CoV-2 vaccine is currently available for newborns.
For the window period before routine vaccination of the newborn, passive
immunization for neonates from vertical transmission can be present for
up to six months.(11)
Transplacental transfer of SARS-CoV-2 antibodies, specifically against
the receptor binding domain (RBD) of the spike protein (anti-S) and
nucleocapsid antigen (anti-N), has been observed in previous studies of
both infected pregnant individuals and those vaccinated against
COVID-19.(12-17) However, the relationship between the timing of
vaccination or infection and transplacental antibody transfer is
unclear.
Given that newborn protection from infectious diseases depends on
antibodies acquired transplacentally,(9) we investigated the timing of
transplacental passage of SARS-CoV-2 antibodies through vaccines and
maternal infections. We focused on a specific, highly vaccinated
pregnant population with or without SARS-CoV-2 infection, solely by the
Omicron strain.