Effectiveness of Maternal Vaccination With mRNA COVID-19 Vaccine During Pregnancy Against COVID-19–Associated Hospitalization in Infants Aged <6 Months

17 States, July 2021-January 2022

Natasha B. Halasa, MD; Samantha M. Olson, MPH; Mary A. Staat, MD; Margaret M. Newhams, MPH; Ashley M. Price, MPH; Julie A. Boom, MD; Leila C. Sahni, PhD; Melissa A. Cameron, MD; Pia S. Pannaraj, MD; Katherine E. Bline, MD; Samina S. Bhumbra, MD; Tamara T. Bradford, MD; Kathleen Chiotos, MD; Bria M. Coates, MD; Melissa L. Cullimore, MD; Natalie Z. Cvijanovich, MD; Heidi R. Flori, MD; Shira J. Gertz, MD; Sabrina M. Heidemann, MD; Charlotte V. Hobbs, MD; Janet R. Hume, MD; Katherine Irby, MD; Satoshi Kamidani, MD; Michele Kong, MD; Emily R. Levy, MD; Elizabeth H. Mack, MD; Aline B. Maddux, MD; Kelly N. Michelson, MD; Ryan A. Nofziger, MD; Jennifer E. Schuster, MD; Stephanie P. Schwartz, MD; Laura Smallcomb, MD; Keiko M. Tarquinio, MD; Tracie C. Walker, MD; Matt S. Zinter, MD; Suzanne M. Gilboa, PhD; Kara N. Polen, MPH; Angela P. Campbell, MD; Adrienne G. Randolph, MD; Manish M. Patel, MD


Morbidity and Mortality Weekly Report. 2022;71(7):264-270. 

In This Article


During July 2021–January 2022, maternal completion of a 2-dose primary mRNA COVID-19 vaccination series during pregnancy was associated with reduced risk for COVID-19 hospitalization among infants aged <6 months in a real-world evaluation at 20 U.S. pediatric hospitals during a period of Delta and Omicron variant circulation. Among 176 infants aged <6 months hospitalized with COVID-19, 148 (84%) were born to mothers who were not vaccinated during pregnancy. Although booster doses are recommended for pregnant women, VE of maternal booster doses received during pregnancy could not be assessed because of small sample size, which likely underestimated VE. Overall, these findings indicate that maternal vaccination during pregnancy might help protect against COVID-19 hospitalization among infants aged <6 months.

COVID-19 during pregnancy is associated with severe illness and death,[7] and pregnant women with COVID-19 are more likely to experience preterm birth, stillbirth, and other pregnancy complications.[8] Vaccination is recommended for pregnant women to prevent COVID-19, including severe illness and death. COVID-19 vaccination is safe and effective when administered during pregnancy.[9,10] Receipt of COVID-19 vaccination during pregnancy is associated with detectable maternal antibodies in maternal sera at delivery, breast milk, and infant sera indicating transfer of maternal antibodies.[3–5] The higher VE point estimates among infants born to women vaccinated later in pregnancy are consistent with the possibility of transplacental transfer of SARS-CoV-2–specific antibodies that might provide protection to infants. The optimal timing of maternal vaccination for the transfer of antibodies to protect the infant is currently uncertain, and the direct effect of maternal COVID-19 vaccination in preventing severe COVID-19 in infants has not previously been described. Further, with infants not currently age-eligible for vaccination and infant hospitalization rates remaining at the highest levels of the pandemic,*** this study suggests that maternal COVID-19 vaccination during pregnancy might protect infants aged <6 months from COVID-19–related hospitalization.

The findings in this report are subject to at least seven limitations. First, VE could not be assessed directly against specific variants. Second, the sample was too small to assess VE by pregnancy trimester of vaccination, and the small sample size resulted in wide confidence intervals for some estimates that should be interpreted with caution. Third, the analysis did not assess whether pregnant women were infected with SARS-CoV-2 before or during pregnancy, which might have provided maternal antibodies. Fourth, residual confounding such as additional differences in behaviors between vaccinated and unvaccinated mothers, including whether mothers had prenatal care, that might affect risk for infection cannot be excluded, and potential confounders (e.g., breastfeeding, child care attendance, and prematurity) could not be accounted for in the model because this information was not available for all infants. Fifth, because this analysis included self-reported data for a few participants, maternal vaccination status might be misclassified for a few infants, or there might be imperfect recollection of whether the mother completed COVID-19 vaccination during pregnancy. Sixth, immunocompromising maternal conditions were not collected to determine whether mothers needed an additional mRNA COVID-19 vaccine dose to complete their primary series. Finally, VE of maternal booster doses received during pregnancy could not be assessed because of small sample size.

Completion of a 2-dose primary mRNA COVID-19 vaccination series during pregnancy was associated with reduced risk for COVID-19–associated hospitalization among infants aged <6 months, and protection was higher among infants whose mothers were vaccinated later in pregnancy. Additional evaluation should examine timing of vaccination before pregnancy compared with during pregnancy. CDC recommends that women who are pregnant, are breastfeeding, are trying to get pregnant now, or might become pregnant in the future get vaccinated and stay up to date with COVID-19 vaccination.†††