Associations between maternal COVID-19 vaccination and infant hospitalization

In a recent study published in The New England Journal of Medicineresearchers evaluated the effectiveness of maternal messenger ribonucleic acid (mRNA) vaccinations during pregnancy against hospitalization for coronavirus disease 2019 (COVID-19) in infants younger than 6 months of age.

Study: Maternal vaccination and risk of hospitalization for Covid-19 in infants. Image Credit: BaLL LunLa/Shutterstock


Infants younger than six months are at increased risk of complications from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and are not eligible to receive COVID-19 vaccines. Transplacental transfers of maternal anti-SARS-CoV-2 antibodies after vaccination of mothers against SARS-CoV-2 could confer immune protection to their infants against SARS-CoV-2.

The authors of the present study previously reported that the risk of COVID-19-associated hospitalization was 61% lower in infants under 6 months of age born to mothers who received double vaccination (mRNA) during pregnancy when the SARS-CoV-2 Delta (B.1.617.2) variant was dominant.

About the study

In the present case-control study, the researchers extended their previous analysis by exploring the protective role of mRNA vaccination of pregnant women against COVID-19-associated hospitalization in infants

The study was conducted between July 1, 2021 and March 8, 2022 and included infants with COVID-19 associated hospitalizations (case infants) and infants without COVID-19 associated hospitalizations (control infants) at 30 pediatric hospitals of 22 states. The infant cases were identified using ongoing active surveillance data from the centers for disease control and prevention (CDC) – funded to overcome the COVID-19 network.

Data were obtained on demographic parameters, history of COVID-19, and clinical outcomes of existing disease via electronic medical records and by interviewing parents (or guardians) of infants. Maternal vaccination information such as vaccination dates, doses received, whether mothers were vaccinated during pregnancy, site where mothers were vaccinated, vaccine manufacturers, and availability of COVID-19 vaccination cards have been obtained.

Data was also obtained for hospitalizations associated with COVID-19, intensive care unit (ICU) admissions and critical cases of COVID-19 requiring life-saving interventions or resulting in death. Life-sustaining interventions included noninvasive mechanical ventilation (continuous or bilevel positive airway pressure), invasive mechanical ventilation, vasoactive infusions, and extracorporeal membrane oxygenation.

All infant cases were diagnosed positive for SARS-CoV-2 by antigen testing or reverse transcription-polymerase chain reaction (RT-PCR) within ten days of symptom onset or three days after hospitalization. Mothers were considered fully vaccinated if they received double doses of mRNA-1273 or BNT162b2 vaccines.

Women who received the initial dose of vaccine before pregnancy and the second dose of vaccine after pregnancy were included in the analysis. Since protective immunity builds after approximately two weeks of vaccination, cases of infants born to mothers vaccinated less than 14 days before delivery were excluded from the analysis.

Additionally, infants born to mothers who received mRNA triple vaccination (n = 29 infants) or who were vaccinated with the Ad26.COV2.S vaccine without mRNA (n = 13 infants) were excluded due to the low number of pregnant women in these two categories. Vaccine efficacy was estimated by comparing the odds of COVID-19 severity in the two groups of infants born to fully immunized mothers during pregnancy in the Delta-predominant periods (between July 1, 2021 and December 18, 2021) and Omicron-dominant (between December 19, 2021 and March 8, 2022).


The analysis was performed for 537 and 512 case and control infants, respectively. Of the infant cases, 181 infants were hospitalized for Delta infections and 356 infants were hospitalized for Omicron infections. The average age of study participants was two months. About 16% and 29% of case infants and control infants, respectively, are born to women fully vaccinated during pregnancy.

Compared to cases of infants born to mothers who were not fully immunized during pregnancy (n=450 infants), cases of infants born to women fully immunized during pregnancy (n=87 infants) had lower admissions in ICU (23% versus 13%). Additionally, infants had lower critical SARS-CoV-2 infection (12% versus 9%), invasive mechanical ventilation requirements (7% versus 3%), noninvasive mechanical ventilation requirements (8 % versus 6%) and vasoactive ventilation infusion requirements (3% versus 1%) compared to control infants.

Of the infant cases, 21% (n=113) were admitted to intensive care, of which 12% (n=64) received vasoactive infusions or mechanical ventilation. The deaths of two case infants due to COVID-19 have been reported, and two case infants required extracorporeal membrane oxygen supplementation, neither of whose mothers received mRNA double vaccination during her pregnancy.

The efficacy of complete maternal mRNA vaccinations against COVID-19-associated hospitalization in infants has been reported to be 52%, with 80% efficacy during Delta-dominance and 38% efficacy during Omicron-dominance . Efficacy was 70% against ICU admission associated with COVID-19 and 47% against hospitalization not requiring ICU admission. Furthermore, the effectiveness was 38% and 69% when mothers were vaccinated during the first 20 weeks of gestation and after 20 weeks of gestation, respectively.

Overall, the study results showed that maternal full (double dose) mRNA vaccination reduced the risk of COVID-19-associated hospitalizations in infants younger than 6 months.

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