1. Vaccination during pregnancy with two doses of mRNA vaccine was associated with reduced risk of hospitalization, intensive care unit (ICU) admission, and severe infection due to coronavirus disease 2019 (COVID-19) in infants.

2. Vaccination after 20 weeks of pregnancy was more effective against infant hospitalization due to all measured COVID-19 strains compared to vaccination prior to 20 weeks of pregnancy.

Evidence Rating Level: 2 (Good)

Study Rundown: Pregnant patients with COVID-19 are at elevated risk of severe illness, hospitalization, and death than those infected in the general population. COVID-19 during pregnancy is also associated with more adverse pregnancy outcomes and neonatal complications. Maternal vaccination may benefit infants as maternal antibodies have been detected in cord blood, breast milk, and infant serum specimens. Accordingly, the present study compared COVID-19 outcomes in infants of vaccinated and unvaccinated patients. Infants whose mothers were fully vaccinated during pregnancy with two doses of mRNA vaccinations had lower incidences of ICU admission, critical COVID-19, need for mechanical ventilation, and need for vasoactive infusions. The effectiveness of maternal vaccination on infant COVID-19 incidence was higher during the period of delta strain predominance than omicron predominance. Additionally, after 20 weeks of pregnancy, maternal vaccination was more effective than before 20 weeks. One of the major limitations was the demographic differences between the case and control groups, which could not account for exposure to specific COVID-19 variants. Further, the history of breastfeeding and health behaviors varied between the vaccinated and unvaccinated groups. This could lead to confounding of the results, as these characteristics can may the vulnerability of infants to COVID-19.

Click to read the study in NEJM

Relevant Reading: Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons

In-Depth [case-control study]: The present case-control, test-negative study aimed to assess the effectiveness of maternal vaccination against adverse outcomes of COVID-19 in infants six months old and younger. Maternal vaccination was defined as having received two doses of mRNA vaccinations against COVID-19. Case infants were identified through electronic medical records for admissions with COVID-19 as the primary diagnosis and a positive SARS-CoV-2 reverse-transcriptase-polymerase-chain reaction (RT-PCR) or antigen test. Control infants were identified as having a negative SARS-CoV-2 RT-PCR while being hospitalized. The final analysis included 537 case infants and 512 control infants. Of the 537 case infants, 113 (21%) were admitted to ICU, including 64 (12%) who required mechanical ventilation or vasoactive infusions. Case infants whose mothers had been fully vaccinated during pregnancy had a lower incidence of ICU admission (23% vs. 13%) and critical COVID-19 (12% vs 9%) as compared to controls. The effectiveness of maternal vaccination against COVID-19-associated hospitalization was 52% (95% Confidence Interval [CI], 33% to 65%). The effectiveness against admission into the ICU was 47% (95% CI, 25% to 62%) and 47% (95% CI, 25% to 62%) for non-ICU hospitalization. Specifically, effectiveness was 80% (95% CI, 60% to 90%) during the period that the delta strain predominated and 38% (95% CI, 8% to 58%) during omicron predominance. Finally, the effectiveness against COVID-19 hospitalization was higher at 68% (95% CI, 50% to 80%) when maternal vaccination occurred after 20 weeks of pregnancy compared to prior. When patients were vaccinated prior to 20 weeks of pregnancy, the effectiveness was 38% (95% CI, 3% to 60%). In summary, maternal vaccination may improve outcomes of infant COVID-19 infection.

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