COVID-19 vaccination and boosting during pregnancybenefits pregnant people and newborns

NIH/National Institute of Allergy and Infectious Diseases(August 11, 2023)

Receiving a COVID-19 mRNA vaccine or booster during pregnancy can benefit pregnant
people and their newborn infants, according to findings recently published in Vaccine. The
paper describes results from the Multisite Observational Maternal and Infant Study for
COVID-19 (MOMI-VAX), which was funded by the National Institute of Allergy and
Infectious Diseases (NIAID), part of the National Institutes of Health.

The MOMI-VAX study launched in June 2021 when data on COVID-19 vaccination in
pregnant people were sparse. Researchers hoped to understand the immune response following
receipt of Pfizer and Moderna COVID-19 vaccines, and determine how much protection
against illness they provided. Pregnant people are more likely to be hospitalised and die from
severe COVID-19, and the disease puts them at greater risk for preterm birth.

Researchers also suspected that, as with other vaccines, the antibodies generated by COVID19 vaccination might transfer to foetuses across the placenta, which would provide newborns
with some additional protection against COVID-19 in their first months of life. Among other
metrics, the study tracked the COVID-19 antibody levels of pregnant people who received
either of the two COVID-19 vaccines, as well as the antibodies in their cord blood when they
gave birth.

Researchers at the NIAID-funded Infectious Diseases Clinical Research Consortium (IDCRC)
followed more than 500 pregnant volunteers and their newborns, at nine study sites. Results
from 240 participants are reported in this paper, including 167 pregnant participants who
received the two-dose primary series of either of the two mRNA vaccines during pregnancy,
and 73 who received a booster dose; at the time, only one booster dose was recommended.
Researchers examined blood samples taken before and after participants were vaccinated or
boosted, and at time of delivery. The researchers also analysed participants’ cord blood at the
time of birth.

The researchers found that pregnant people who received the COVID-19 vaccines generated
antibodies against specific types of SARS-CoV-2. These included antibodies against the
D614G variant (which the vaccines were designed to protect against), as well as the Delta and
Omicron sub variants. The antibodies effectively crossed the placenta and were also found in
the cord blood of vaccinated participants. This likely conferred some protection in the
newborns against these variants immediately after birth — a critical time when they are
vulnerable to severe COVID-19 disease but are too young to be vaccinated, according to the

Pregnant participants who received a booster dose had substantially more antibodies against
SARS-CoV-2, both in their own blood and in their cord blood, suggesting that boosting also
increased their newborns’ immune defences against COVID-19. These findings support the use
of COVID-19 vaccination, and in particular booster doses, during pregnancy for protection of
mothers and newborns.

The researchers suggest that future studies could determine the best time during pregnancy to
get vaccinated against COVID-19 to provide the most protection for parent and newborn. In
addition, researchers hope to build a more complete picture of how prenatal COVID-19
vaccination affects infants using more data collected during the MOMI-VAX study, such as
antibody levels in breastmilk and infants’ SARS-CoV-2 antibody levels in the year after birth.

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