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Source:

WHO. Definition and categorization of the timing of mother-to-child transmission of SARS-CoV-2. https://www.who.int/publications/i/item/WHO-2019-nCoV-mother-to-child-transmission-2021.1. Accessed February 9, 2021.

Disclosures: Kimberlin reports being an ex officio member of the AAP Committee on Infectious Diseases and a member of the writing group for AAP Neonatal COVID guidance. Puopolo reports being a member of the AAP Committee on Fetus and Newborn and a member of the writing group for the AAP Neonatal COVID-19 guidance. Gyamfi-Bannerman reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
February 09, 2021
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Vertical transmission of SARS-CoV-2 possible but ‘not common’

Source:

WHO. Definition and categorization of the timing of mother-to-child transmission of SARS-CoV-2. https://www.who.int/publications/i/item/WHO-2019-nCoV-mother-to-child-transmission-2021.1. Accessed February 9, 2021.

Disclosures: Kimberlin reports being an ex officio member of the AAP Committee on Infectious Diseases and a member of the writing group for AAP Neonatal COVID guidance. Puopolo reports being a member of the AAP Committee on Fetus and Newborn and a member of the writing group for the AAP Neonatal COVID-19 guidance. Gyamfi-Bannerman reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
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A WHO working group said this week that it found “limited evidence” concerning the timing of vertical transmission of SARS-CoV-2 or the extent to which it happens, although studies have demonstrated that it is possible.

The group, which included experts in obstetrics, neonatology, pediatrics, epidemiology, virology, infectious disease, congenital infections and placental pathology, reviewed findings available through Oct. 7.

Source: Shutterstock.com
Source: Shutterstock.com

“Defining vertical transmission of SARS-CoV-2 based on reports in the literature to date has been difficult,” they wrote. “Most reports of vertical transmission have been based on a single positive neonatal RT-PCR in an upper respiratory tract specimen, with significant variation in the timing of sample collection.”

The authors said the “paucity of data” on the subject “is partly due to the lack of standardized definitions which would allow comparisons of data from different studies.” They proposed a classification system based on documented maternal infection and testing to evaluate the timing of vertical transmission.

“The mechanism by which potential in utero acquired fetal infection would result in neonatal naso- or oro-pharyngeal positivity is unclear,” they wrote. “The specificity of SARS-CoV-2 positive placental or amniotic fluid specimens alone to represent in utero infection is unclear, and the utility of SARS-CoV-2 IgM/IgA alone to diagnose neonatal infection is problematic given reports of positive IgM tests in asymptomatic neonates who have tested negative by nasopharyngeal RT-PCR. Thus, a combination of initial and confirmatory tests is required in the classification system to determine infection occurrence and timing.”

‘Unlikely’ but possible

Findings published last October in two journals showed the possibility, though unlikely, of vertical transmission of SARS-CoV-2 to newborns.

Cynthia Gyamfi-Bannerman

Cynthia Gyamfi-Bannerman, MD, MSc, a maternal-fetal medicine specialist at Columbia University, and colleagues assessed 101 newborns in their first 25 days of life to determine whether mothers with perinatal SARS-CoV-2 infection had transferred the virus to them.

From March 13 to April 24, 100 women delivered 101 infants, including one set of twins. Of these women, 99 tested positive for SARS-CoV-2, whereas one tested negative but was treated as if she had COVID-19 because she had similar symptoms. The median age of the women was 28.5 years, with 90 women being asymptomatic or with mild symptoms and the remaining having severe symptoms.

Of the 101 infants, 15 were tested within their first 24 hours of life, 79 by their 48th hour and the remaining seven after that. There was a total of 141 tests administered, with 70 infants needing to be tested only once.

Of the 141 specimens, researchers did not detect SARS-CoV-2 viral RNA in 135 of them. Overall, the incidence of transmission was 2% (95% CI, 0.2%-7%) in two newborns, the researchers reported.

The newborns “had indeterminate test results, indicative of low viral load ... [one] never underwent retesting but remained well on follow-up, and the other had negative results on retesting,” the authors wrote.

“This study shows both that clinical vertical transmission is unlikely, and that if it occurs, it is not likely to have short-term clinical significance,” Gyamfi-Bannerman told Healio.

“We think that vertical transmission is possible, but we think it is not common,” she said. “This is likely why it has taken so long to verify possible transmission with millions of cases worldwide.”

David W. Kimberlin
Karen M. Puopolo

In a related editorial, David W. Kimberlin, MD, co-director of the division of pediatric infectious diseases at Children’s of Alabama, and Karen M. Puopolo, MD, PhD, chief of newborn pediatrics at Children’s Hospital of Philadelphia, said the study provided “a good example of how careful observations can improve our understanding of what was previously unknown and can help inform treatment recommendations.”

“We can draw solace from the knowledge that scientific processes that have worked in the past are working now and will continue to serve us as we move together into an uncertain future,” they wrote.

Second study

Claudio Fenizia

In another study published in Nature, Claudio Fenizia, PhD, of the University of Milan, and colleagues analyzed maternal and newborn samples from nasopharyngeal swabs, vaginal swabs, maternal and umbilical cord plasma, placenta and umbilical cord biopsies, amniotic fluid and milk from 31 SARS-CoV-2-infected mothers.

Of the 31 women, four were classified with severe cases, with one needing postpartum admission to the ICU. Thirty of the 31 pregnancies were delivered at full term. Two of the newborns were diagnosed with SARS-CoV-2 upon delivery through nasopharyngeal swabs, the researchers reported, and one of them tested negative 48 hours later.

“Our results suggest in utero vertical transmission in two of the 31 (6%) enrolled SARS-CoV-2-positive women,” the authors wrote. “One case was characterized by a severe clinical outcome, while the other case was classied as mild; we speculate that the risk of mother-to-child viral transmission does not directly depend on the severity of disease progression.”

The AAP has said it is OK for SARS-CoV-2-infected mothers to be with newborns after birth, and evidence has shown they are unlikely to infect newborns while rooming-in. Transmission of SARS-CoV-2 through breast milk is also thought to be unlikely.

References:

Dumitriu D, et al. JAMA Pediatr. 2020:doi.10.1001/jamapediatrics.2020.4298.

Fenizia C, et al. Nature. 2020:doi.10.1038/s41467-020-18933-4.

Kimberlin DW, et al. JAMA Pediatr. 2020:doi.10.1001/jamapediatrics.2020.4304.

WHO. Definition and categorization of the timing of mother-to-child transmission of SARS-CoV-2. https://www.who.int/publications/i/item/WHO-2019-nCoV-mother-to-child-transmission-2021.1. Accessed February 9, 2021.