In a first of its kind study, researchers found women who received two mRNA COVID vaccine doses during pregnancy were 61% less likely to have a baby hospitalized for COVID-19 during the first 6 months of life.
In addition, two doses of the Pfizer/BioNTech or Moderna COVID vaccine later in a pregnancy were linked to an even higher level of protection, 80%, compared with 32% when given before 20 weeks’ gestation.
This finding suggests a greater transfer of maternal antibodies closer to birth, but more research is needed, cautioned senior study author Manish Patel, MD, during a Tuesday media telebriefing held by the Centers for Disease Control and Prevention.
Unanswered questions include how the babies got infected or if there is any protection afforded to babies for women vaccinated before pregnancy.
“We cannot be sure about the source of the infection,” said Dr. Patel, a medical epidemiologist with the CDC COVID-19 Emergency Response Team.
Dana Meaney-Delman, MD, MPH, agreed, but added that “perinatal transmission of the virus is very rare” with SARS-CoV-2. She is a practicing obstetrician and gynecologist and chief of the CDC Infant Outcomes Monitoring Research and Prevention Branch.
The study numbers were too small to show if a booster shot during pregnancy or breastfeeding could provide even greater protection for babies, Dr. Patel said.
The early release study was published online Feb. 15 in the CDC’s Morbidity and Mortality Weekly Report (MMWR).
Many previous studies looking at COVID-19 immunization during pregnancy focused on maternal health and “have clearly shown that receiving an mRNA COVID-19 vaccine during pregnancy reduces the risk for severe illness,” Dr. Meaney-Delman said.
Some dual protection suggested
Now there is evidence for a potential benefit to babies as well when a pregnant woman gets vaccinated. The study “provides real-world evidence that getting COVID-19 vaccination during pregnancy might help protect infants less than 6 months [of age],” Dr. Meaney-Delman said.
“These findings continue to emphasize the importance of COVID-19 vaccination during pregnancy to protect people who are pregnant and also to protect their babies,” she said.
Dr. Patel and colleagues studied 379 infants younger than 6 months hospitalized between July 1, 2021 and Jan. 17 of this year. Delta and then the Omicron variant predominated during this time.
The infants were admitted to one of 20 children’s hospitals in 17 states. The researchers compared 176 infants admitted with a positive COVID-19 PCR test to another 203 infants with a negative PCR test who served as controls.
Half as many mothers of infants admitted with COVID-19 were vaccinated during pregnancy, 16%, versus 32% of mothers of the control infants.
Vaccination with two doses of mRNA vaccine during pregnancy was 61% effective (95% confidence interval, 31%-78%) at preventing hospitalization among these infants. Because the study was epidemiological, the lower risk was an association, not a cause-and-effect finding, Dr. Patel said.
Babies admitted to the hospital positive for COVID-19 were more likely to be non-Hispanic Black, 18%, versus 9% of control group babies; and more likely to be Hispanic, 34% versus 28%, respectively.
A total 24% of infants with COVID-19 were admitted to the ICU, including the baby of an unvaccinated mother who required extracorporeal membrane oxygenation (ECMO). Another baby of an unvaccinated mother was the only infant death during the study.
Maternal vaccination trends
A reporter pointed out that COVID-19 vaccination rates tend to be low among pregnant women. “So there is some exciting news,” Dr. Meaney-Delman said, referring to a steady increase in the percentages of pregnant women in the U.S. choosing to get vaccinated, according to the CDC Data Tracker website.
“The numbers are encouraging, [but] they’re not quite where we need them to be, and they do differ by race and ethnicity,” she added.
A version of this article first appeared on Medscape.com.