Maternal vaccination lowers risk of COVID-19-associated hospitalization in infants: NEJM

USA: Completion of a 2-dose primary mRNA COVID-19 vaccination series during pregnancy is associated with a reduced risk of hospitalization for Covid-19, including for critical illness, among infants aged <6 months, states an article published in The New England Journal of Medicine.

Coronavirus disease (COVID-19), an infectious disease caused by the SARS-CoV-2 virus has affected different people in different ways. Covid-19 during pregnancy is associated with severe illness, hospitalization, and death as well as an increased risk of adverse pregnancy outcomes and neonatal complications. Evidence has shown that COVID-19vaccination before and during pregnancy is safe, effective, and beneficial to both mother and baby.

The mRNA vaccines (BNT162b2 [Pfizer–BioNTech] and mRNA-1273 [Moderna]) have been proved to be highly effective in preventing severe Covid-19 during pregnancy. Infants younger than 6 months of age are at high risk for complications of Covid-19 but are not eligible for vaccination. Maternal Covid-19 vaccination may result in the transplacental transfer of antibodies which may confer protection against SARS-CoV-2 in infants.

Natasha B, Vanderbilt University Medical Center, USA and her colleagues designed a case-control test-negative study to evaluate the effectiveness of maternal vaccination during pregnancy against hospitalization for Covid-19 among infants aged <6 months.

For the study, investigators enrolled 537 infants hospitalized for Covid-19 (case infants) and 512infants hospitalized without Covid-19 (control infants) at 30 hospitals in 22 states (2021-2022). 16% of the case infants and 29% of the control infants had been born to mothers who had been fully vaccinated against Covid-19 during pregnancy. The effectiveness of the vaccine was estimated by comparing the odds of full maternal vaccination (two doses of mRNA vaccine) among case infants and control infants during circulation of the B.1.617.2 (delta) variant and the B.1.1.259 (omicron) variant.

Key findings of the study,

• Among the case infants, 113 (21%) received intensive care (64 [12%] received mechanical ventilation or vasoactive infusions).

• Two case infants died from Covid-19; neither infant's mother had been vaccinated during pregnancy

• The overall effectiveness of maternal vaccination against hospitalization for Covid-19 among infants was 52%, 80% during the delta period, and 38% during the omicron period.

• Effectiveness was 69% when maternal vaccination occurred after 20 weeks of pregnancy and 38% during the first 20 weeks of pregnancy.

Analyzing the results of this real-world evaluation study,  the authors conclude that maternal vaccination with mRNA vaccines is associated with a substantial reduction in the risk of Covid-19–related hospitalization and critical illness among young infants, although reductions were less pronounced when the omicron variant was predominant. Also, the protection was higher among infants whose mothers were vaccinated later in pregnancy.

The findings provide additional support to the current recommendations regarding Covid-19 vaccination during pregnancy, the authors commented.

Reference:

Natasha B. Halasa, M.D., Samantha M. Olson, M.P.H., Mary A. Staat, M.D., Margaret M. Newhams et al. June 22, 2022 DOI: 10.1056/NEJMoa2204399