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

Links between maternal COVID-19 vaccination and hospitalization in infants

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

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


Infants under six months of age are at increased risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection complications and are not eligible to receive COVID-19 vaccines. Transplacental transfers of maternal anti-SARS-CoV-2 antibodies after SARS-CoV-2 vaccination of mothers 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 < 6 months of mothers who received double (mRNA) vaccination 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 hospitalization in infants <6 months during the dominance of the SARS-CoV-2 Omicron (B. 1.1.259) variant. Compared to their previous study, the current study included a much larger sample size, ie more 361 and 309 case babies and control babies, respectively.

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

Data was obtained on demographic parameters, previous COVID-19 history and clinical findings of pre-existing disease through electronic health records and by interviewing the parents (or guardians) of the infants. Maternal vaccination data, such as vaccination dates, doses received, whether the mothers were vaccinated at the pregnancy dose, where mothers were vaccinated, vaccine manufacturers, and availability of the COVID-19 vaccination card.

Data was also obtained for COVID-19-associated hospitalizations, intensive care (ICU) admissions, and critical cases of COVID-19 requiring life-sustaining interventions or leading to death. Life support interventions include non-invasive mechanical ventilation (continuous or bilevel positive airway pressure), invasive mechanical ventilation, vasoactive infusions, and extracorporeal membrane oxygenation.

All infants were diagnosed as SARS-CoV-2 positive by antigen testing for 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 had received double doses of the mRNA-1273 or BNT162b2 mRNA vaccines.

Women who received the initial vaccine dose before pregnancy and the second vaccine dose after pregnancy were included in the analysis. Since protective immunity is built after approximately two weeks of vaccination, infants born to mothers 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 in both categories. . Vaccine efficacy was estimated by comparing the probability of the severity of COVID-19 in both infant groups of mothers who were fully vaccinated during pregnancy during the periods of Delta domination (between July 1, 2021 and December 18, 2021) and Omicron – domination (between December 19, 2021 and March 8, 2022).


The analysis was performed for 537 and 512 infants and control infants, respectively. Of the case babies, 181 infants were hospitalized with Delta infections and 356 infants were hospitalized with Omicron infections. The mean age of the study participants was two months. Approximately 16% and 29% of the infants and control infants, respectively, were born to women who had been fully vaccinated during pregnancy.

Compared to case babies born to mothers who were not fully vaccinated during pregnancy (n=450 babies), case babies born to women who were fully vaccinated during pregnancy (n=87 babies) showed lower IC admissions (23% vs. 13%). In addition, case babies showed a lower critical SARS-CoV-2 infection (12% vs 9%), invasive mechanical ventilation requirements (7% vs 3%), non-invasive mechanical ventilation requirements (8% vs 6%) and vasoactive infusion requirements (3% vs 1%) compared to control infants.

Of the infants, 21% (n=13) were admitted to the ICU, of which 12% (n=64) received vasoactive infusions or mechanical ventilation. The deaths of two infants from COVID-19 were reported, and two infants required extracorporeal membrane oxygen supplementation, none of whose mothers received double mRNA vaccination while pregnant.

The efficacy of complete maternal mRNA vaccinations against COVID-19-associated hospitalization in infants was reported to be 52%, with 80% efficacy during Delta predominance and 38% efficacy during Omicron predominance. Efficacy was 70% against COVID-19-related ICU admission and 47% against hospitalization that did not require ICU admission. Furthermore, the efficacy 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 findings showed that complete (double dose) maternal mRNA vaccination reduced the risk of COVID-19-associated hospitalizations in infants under 6 months of age.

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