Researchers have provided additional evidence that vaccination against COVID-19 during pregnancy helps protect young infants.

The findings of a new study sponsored by the Centers for Disease Control and Prevention were published in the New England Journal of Medicine. Infant risk of hospitalisation for COVID-19 had reduced by 80 per cent during the Delta wave, July 1 - December 18, 2021, and by 40 per cent during the Omicron wave, December 19 - December 8, 2022.

"Our results reinforce the importance of COVID-19 vaccination during pregnancy to protect both the women and their babies from COVID-19," said co-author Bria Coates, MD, critical care physician at Ann & Robert H. Lurie Children's Hospital of Chicago and assistant professor of paediatrics at Northwestern University Feinberg School of Medicine.

"Although protection was lower during the Omicron period, compared to the Delta period, even a moderate reduction in risk is important, because COVID-19 vaccines are not likely to be available for babies younger than 6 months old in the foreseeable future," it said.

The study included infants younger than 6 months of age who were admitted to 30 pediatric hospitals in 22 states from July 1, 2021, to March 8, 2022. Dr Coates and colleagues found that most infants (90 per cent) who needed intensive care due to COVID-19 infection were born to mothers who were not vaccinated during pregnancy.

Infants aged younger than 6 months old are at high risk for complications of COVID-19, including severe respiratory failure or death and account for a disproportionately high percentage of hospitalisations among those aged 0-4 years.

This study included data on 537 babies who were hospitalised with COVID-19. Of those, 21 per cent were admitted to the intensive care unit and 12 per cent required mechanical ventilation, extra help getting enough oxygen to the body, or vasoactive infusions.

Two babies died because of COVID-19 and two required advanced life support that helps the body get enough oxygen; the mothers of these babies were not vaccinated.

Researchers also found that the effectiveness of maternal COVID-19 vaccination against COVID-19 hospitalisation for babies was higher among women vaccinated after 20 weeks of pregnancy, versus early in pregnancy.

"While protection for the baby is important, it is critical to remember that COVID-19 vaccines protect women against severe illness during pregnancy and reduce complications from COVID-19," said Dr Coates, who also is the crown family research scholar in Developmental Biology.

When considering the timing of COVID-19 vaccination during pregnancy, the CDC and professional medical organisations, like the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, recommend COVID-19 vaccination as soon as eligible and at any point in pregnancy.

The CDC recommends that women who are pregnant, breastfeeding, trying to get pregnant, or might become pregnant in the future get vaccinated and stay up to date with their COVID-19 vaccines.

Research at Ann & Robert H. Lurie Children's Hospital of Chicago is conducted through Stanley Manne Children's Research Institute. The Manne Research Institute is focused on improving child health, transforming pediatric medicine and ensuring healthier futures through the relentless pursuit of knowledge.

Lurie Children's is ranked as one of the nation's top children's hospitals by U.S. News & World Report. It is the pediatric training ground for Northwestern University Feinberg School of Medicine.