Study reveals low COVID-19 transmission rate from mothers to newborns

A study by KK Women's and Children's Hospital (KKH), Singapore General Hospital (SGH) and National University Hospital (NUH) has revealed that COVID-19 transmission from mothers to their newborns is low. The study has been published in Annals of the Academy of Medicine, Singapore.

The study involving 371 women, who had COVID-19 infection during pregnancy, and their newborns found that only four infants or 1.1% of the babies were diagnosed with COVID-19 after birth, of which three (1.1%) were from mothers who were COVID-19 vaccinated and one infant (1.3%) was from a mother who was not vaccinated.

Senior Author of the study, Dr. Yeo Kee Thai, Senior Consultant, Department of Neonatology, KKH said, "Our study assures expectant parents and health care professionals that COVID-19 transmission from mother to baby is extremely low. In comparison to international reports, the incidence of transmission is also at a much lower rate. This is likely attributed to the higher vaccination rate among our pregnant population, which also explains the comparatively lower occurrence of moderate to severe symptoms and a lesser need for interventions in vaccinated pregnant women who were infected with COVID-19.

Vaccinated pregnant women infected with COVID-19 were found to have milder disease effects (1.8% moderate/severe disease vs. 8% moderate/severe disease) and were less likely to require intensive care as compared to unvaccinated pregnant women who were infected (1.4% vs. 8%). Among the group, one of the unvaccinated pregnant patient who was infected with COVID-19 had required extracorporeal membrane oxygenation (ECMO) support.

The study also found that pregnant women infected with the omicron variant had milder symptoms (98.3% vs. 92.3%), and were less likely to require intensive care (1.0% vs. 9.0%), or need mechanical ventilation (0.3% vs. 3.8%) as compared to those infected with non-omicron variants.

Newborns of pregnant women infected with the omicron variant were also less likely to require intensive care (3.8% vs. 14.1%).

This study is part of KKH's ongoing efforts to build evidence-based perspectives for the limited studies on COVID-19 in Singapore and Asia. The study took place from December 2019 to February 2022, covering the period from when the virus was first identified to the emergence of the omicron variant in late 2021. Based on timing of the infections and the reported circulating variants, the identified variants were Wild-type (2.2%), Alpha (0.8%), Delta (18.1%) and omicron (79.9%).

The research participants were categorized into two groups—vaccinated and unvaccinated—as COVID-19 vaccination was made available to pregnant women in June 2021. Among the 353 pregnant women who provided their COVID-19 vaccination status, 278 (78.8%) had received one or more dose before or during their pregnancy and 75 (21.2%) were unvaccinated.

Dr. Yeo added, "As we appreciate these encouraging findings, pregnant women remain a vulnerable group susceptible to severe outcomes from SARS-CoV-2. Hence, it is crucial that our pregnant women keep up to date with their COVID-19 vaccination, to keep their families safe."

While this study was not designed to focus on the effects of maternal COVID-19 vaccination in newborns, other studies including an earlier KKH-led study revealed that COVID-19 vaccination during pregnancy was found to be up to 44.4% effective in protecting infants against SARS-CoV-2 infection up to six months after birth.