Associations between maternal COVID-19 vaccination and hospitalization in infants

In a recently published study in The New England Journal of MedicineResearchers examined the effectiveness of maternal messenger ribonucleic acid (mRNA) vaccination during pregnancy compared to hospitalization for coronavirus disease 2019 (COVID-19) in infants <6 months of age.

Study: Maternal Vaccination and Hospitalization Risk for Covid-19 in Infants. Credit: BaLL LunLa/Shutterstock


Infants younger than six months are at increased risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and are ineligible to receive COVID-19 vaccines. Transplacental transmission of maternal anti-SARS-CoV-2 antibodies after maternal SARS-CoV-2 vaccination could confer immune protection against SARS-CoV-2 on their infants.

The authors of the present study previously reported that the risk of COVID-19-associated hospitalization was 61% lower in infants <6 months of age born to mothers who received dual 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, researchers extended their previous analysis by examining the protective role of mRNA vaccination of pregnant women against COVID-19-associated hospitalizations in infants aged <6 months during SARS-CoV-2 dominance Omicron (B.1.1.259) variant. Compared to their previous study, the present study included a much larger sample size, ie more 361 and 309 case infants and control infants, respectively.

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) in 30 children’s hospitals out of 22 states. Case children were identified from active ongoing surveillance data from the centers to the disease control and prevention (CDC) – Funded Network to Overcome COVID-19.

Data on demographic parameters, COVID-19 history and clinical findings of the existing condition were collected via electronic medical records and by interviewing the parents (or guardians) of the infants. Maternal immunization information such as immunization dates, doses received, whether the mothers were vaccinated during pregnancy, where the mothers were vaccinated, vaccine manufacturers, and the availability of the COVID-19 vaccination card was obtained.

Data was also collected for COVID-19-associated hospitalizations, intensive care unit (ICU) admissions, and critical COVID-19 cases requiring life support or resulting in death. Life-sustaining interventions included non-invasive mechanical ventilation (continuous or two-stage positive airway pressure), invasive mechanical ventilation, vasoactive infusions, and extracorporeal membrane oxygenation.

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

Women who received the first dose of vaccine before pregnancy and the second dose of vaccine after pregnancy were included in the analysis. Because protective immunity is established after approximately two weeks of vaccination, infants born to mothers who were vaccinated <14 days prior to delivery were excluded from the analysis.

In addition, infants born to mothers who received triple mRNA vaccination (n=29 infants) or who were vaccinated with the Ad26.COV2.S non-mRNA vaccine (n=13 infants) were excluded due to the small number of pregnant women excluded these two categories. Vaccine efficacy was estimated by comparing the likelihood of COVID-19 severity in both groups of infants born to mothers pregnant during the Delta predominance periods (between July 1, 2021 and March 18, 2021). December 2021) and the Omicron Domination (between December 19, 2021 and March 8, 2022).


Analysis was performed for 537 and 512 case infants and control infants, respectively. Among the case children, 181 children were hospitalized with delta infections and 356 children with omicron infections. The average age of the study participants was two months. About 16% and 29% of the case infants and control infants, respectively, were born to women who were fully vaccinated during pregnancy.

Compared to case children born to mothers who were not fully vaccinated during pregnancy (n = 450 infants), case children born to women who were fully vaccinated during pregnancy (n = 87 infants) had a fewer intensive care units (23% vs. 13%). In addition, case children showed 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 infusion requirements (3rd % vs. 1%) compared to control children.

Of the case children, 21% (n=113) were admitted to the ICU, of whom 12% (n=64) were receiving vasoactive infusions or mechanical ventilation. The deaths of two case children due to COVID-19 were reported and two case children required extracorporeal membrane oxygen supplementation, none of the mothers received double mRNA vaccination during pregnancy.

The efficacy of full maternal mRNA immunizations against COVID-19-associated infant hospitalizations has been reported as 52%, with 80% efficacy in Delta predominance and 38% efficacy in Omicron predominance. Efficacy was 70% versus a COVID-19 associated ICU admission and 47% versus a hospitalization that did not require an ICU admission. In addition, the efficacy was 38% and 69% when the mothers were vaccinated during the first 20 weeks of pregnancy and after the 20th week of pregnancy, respectively.

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

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