If mom is vaccinated while pregnant, does it help her baby’s immunity after birth?

Families/Kids Vaccines

New data point toward yes!

We already knew that moms vaccinated during pregnancy pass on anti-spike protein antibodies to their unborn babies that last up to 6 months after birth, and that these antibodies are found in breast milk as well. We also know that vaccinated moms pass on higher amounts of antibodies than moms who have a natural infection during pregnancy.

A new study published in the New England Journal of Medicine on June 22, 2022 by researchers at Vanderbilt University found evidence that the sharing of antibodies during pregnancy from mom to baby translates into better protection against severe COVID-19 infection for infants after birth. The mothers included in the study received 2 doses of mRNA vaccines; either both doses during pregnancy or the second dose to complete the series during their pregnancy.

Data for this study was collected between July 2021 and March 2022 from 30 hospitals in 22 states, spanning the Delta (July through December 2021) and Omicron (December through March 2022) waves. Researchers used a case-control test-negative design. They compared infants under 6 months of age admitted to the hospital, 537 case infants with COVID-19 and 512 control infants without COVID-19.

🤓 🚨 Nerd alert!: In a case-control study, two very similar groups are compared, one with COVID-19 and one without. But in a case-control test-negative study, both the control group and the study group undergo testing for the same reason, in this case symptoms of COVID-19. Patients with sick symptoms are swabbed for lab testing. People who test positive are defined as cases and those who test negative make up the control group. This is a common study design used to evaluate vaccine efficacy, because it allows researchers to make quick use of broadly collected data, which is particularly helpful when studying a fast-moving virus like COVID-19.

In this study, 16% of the case infants with COVID-19 and 29% of the control infants were born to moms fully vaccinated during pregnancy. In those with COVID-19, 113 infants (21%) required ICU level of care due to severe illness. 2 infants in this group died; neither mom was vaccinated during their pregnancy. According to the results in the article, “the effectiveness of maternal vaccination against hospitalization for COVID-19 among infants was 52% (95% confidence interval, 33 to 65) overall, 80% during the Delta period and 38% during the omicron period”.

Additionally, researchers noted that the effectiveness was higher if mom received her vaccines during the 2nd half of pregnancy, 69% effective, vs. 38% effective if mom was vaccinated during the first half of pregnancy.

Overall, the study shows promising data that risk of hospitalization and also the need for ICU level care was reduced in infants of fully vaccinated moms. Vaccine effectiveness against ICU admission with severe illness was 70% overall. Researchers found that 90% of infants in their study admitted to the ICU for COVID-19 were born to unvaccinated mothers.

There are some limitations to this study. This study did not consider previous infections. Previous infection in moms could increase the estimates of vaccine effectiveness. Also, we can’t apply this research to less severe COVID-19 illness in infants, since the study only looked at those sick enough to be hospitalized. The study also didn’t account for moms who had booster doses, so we don’t know what role a booster plays.

Overall, this study is promising news for some of our tiniest citizens! Since vaccines aren’t approved until babies are older than 6 months, evidence shows vaccinating and protecting mom during her pregnancy also provides lasting protection to her infant – 2 for 1!

We are at our strongest when we use every form of protection we can together – if you are visiting a new baby, continue to mask, wash hands before holding the child, and most importantly, stay away if you feel sick (even if you are COVID negative!).

Stay safe. Stay well.

Love, Those Nerdy Girls

Additional Resources:

NEJM: Maternal Vaccination and Risk of Hospitalization for Infants

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