Vertical COVID-19 transmission low in SG

Transmission of SARS-CoV-2 infection from mothers to newborns appears to be rare in a cohort study conducted by the KK Women’s and Children’s Hospital (KKH), Singapore General Hospital (SGH), and National University Hospital (NUH).

“Our study assures expectant parents and healthcare professionals that COVID-19 transmission from mother to baby is extremely low,” commented senior study author Dr Yeo Kee Thai from KKH, Singapore, in a press release.

The trial was conducted between December 2019 and February 2022 as part of KKH’s ongoing efforts to build evidence-based data owing to the limited literature on COVID-19 in Singapore and Asia. A total of 371 mother-infant pairs from KKH, SGH, and NUH were included. The mums had COVID-19 during pregnancy (median age 31 years; 95 percent had mild disease). [Ann Acad Med Singap 2024;53:53-56]

Participants were categorized as vaccinated or unvaccinated. Of those who provided their COVID-19 vaccination status (n=353), over three-quarters (78.8 percent) had received ≥1 dose before or during their pregnancy; the rest were unvaccinated.

The most common variant identified was Omicron (79.9 percent), followed by Delta (18.1 percent). The least common were wild-type (2.2 percent) and Alpha (0.8 percent).

Four infants (1.1 percent) were diagnosed with COVID-19 after birth. Of these, three (1.1 percent) had mums who were vaccinated; the other one’s mum (1.3 percent) was unvaccinated.

Compared with the unvaccinated cohort, the vaccinated group had a lower incidence of moderate-to-severe disease (1.8 percent vs 8 percent; p=0.01) and were less likely to require admission to the intensive care unit (ICU; 1.4 percent vs 8 percent; p=0.008). These highlight the role of vaccination in reducing the risks of severe outcomes in pregnant women.

The transmission rate was much lower than that seen in international studies, Yeo noted. “This is likely attributed to the higher vaccination rate amongst 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.”

Omicron vs non-Omicron

Women infected with the Omicron variant were less likely to have moderate-to-severe disease than those infected with non-Omicron variants (1.7 percent vs 7.7 percent; p=0.006). ICU admission was also less likely (1 percent vs 9 percent; p<0.001), as was the need for mechanical ventilation (0.3 percent vs 3.8 percent; p=0.008) or extracorporeal membrane oxygenation (0 percent vs 1.3 percent; p=0.2).

These findings underscore the lower pathogenicity of Omicron and thus lower harmful effects in pregnant women compared with other variants, said Yeo and colleagues.

Newborns of mums infected with Omicron were also less likely to require ICU admission (3.8 percent vs 14.1 percent; p=0.001) and more likely to be allowed to room-in with their mums (73.3 percent vs 52.9 percent; p=0.004).

Keep vaccines up-to-date

“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,” Yeo said.

“Risks of poor maternal outcomes, including ICU admissions, can be mitigated by the administration of maternal COVID-19 vaccination and should be encouraged,” Yeo and colleagues noted.