November 19, 2021

expert reaction to study looking at the theoretical possibility of unborn babies contracting COVID-19 from the mother

A study published in BJOG: An International Journal of Obstetrics & Gynaecology looks at COVID-19 and whether transmission could occur from an infected mother to an unborn fetus (vertical transmission). 

Dr Chris Gale, Reader in Neonatal Medicine, Imperial College London, said:

“A very small number of babies have been infected by SARS-CoV-2 through the placenta following maternal infection; but this type of infection is very rare. This study shows a potential route by which transplacental infection might happen, finding babies have receptors in the gut that may allow the virus to gain entry into cells, for example if the virus was present in amniotic fluid. We know from national surveillance however that neonatal infection is rare, and also that when babies are infected with SARS-CoV-2 it is more common for babies to catch the virus after birth, rather than via the placenta. This highlights the importance of immunising pregnant women to protect both them and their babies from SARS-CoV-2 infection.”

Prof Marian Knight FMedSci, Professor of Maternal and Child Population Health & Honorary Consultant in Public Health, University of Oxford, said:

“This laboratory study hypothesises that the fetal intestine may be a route for acquisition of SARS-CoV-2 infection, based on co-expression of proteins which the virus may use to gain entry to cells. The study clearly shows localisation of these proteins in the fetal intestine, based on previously collected samples. However, the research does not demonstrate that infection does occur through this route, and the authors have noted that very few cases of transmission of SARS-CoV-2 between mother and baby in utero have been convincingly demonstrated. Data from UK national surveillance suggest that the majority of infant infections are acquired after birth, and this emphasises the importance of maternal vaccination to prevent fetal or infant infections, as maternal antibodies are known to cross the placenta and protect the baby after birth.”

Dr Victoria Male, Lecturer in Reproductive Immunology, Imperial College London, said:

“We already know that babies can be infected with COVID before they are born, but luckily this is not common. Previous studies have looked at whether the placenta expresses the proteins that would make it vulnerable to being infected with the COVID virus: in the second half of pregnancy, it does not. This study used banked fetal tissue samples to look at the expression of these proteins in a variety of fetal organs. It agrees that the placenta is not likely to be vulnerable to COVID infection in the second half of pregnancy, but notes that the guts of unborn babies are a potential site at which they could get infected. This could occur if the virus gets into the amniotic fluid, and the baby then swallows it.

“Although this study highlights a potential route by which unborn babies could be infected by COVID, expectant parents should feel reassured that in utero COVID infection is uncommon. However, we do know that COVID in pregnancy is associated with an increased risk of preterm birth and stillbirth, so we recommend that pregnant people are vaccinated to protect themselves and their babies. We have extensive data to confirm that COVID vaccination is safe in pregnancy.”

Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“Your immune system can respond to whole viruses, but it can also respond to viral fragments that might be released as an infected woman fights off the infection, and some of these fragments may well be small enough to pass across the placenta and generate an antibody response. We also know that mothers’ antibodies can also cross the placenta. This is an important mechanism that can protect baby from several diseases. Even if a new-born baby has antibodies to coronavirus, it doesn’t mean it has been infected.

“Yes, a baby has the necessary receptors in the gut to allow virus infection, but the virus has to get there to be able to infect. And that’s the rub. The placenta is a good barrier to prevent the virus crossing into baby’s bloodstream or into the amniotic fluid, and that’s why infection of a baby during pregnancy is so rare.

Dr Julian Tang, Honorary Associate Professor/Clinical Virologist, University of Leicester, said:

“In a sense these findings are nothing new – several studies suspected and/or found evidence of SARS-COV-2 vertical transmission previously:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7392880/

https://www.nature.com/articles/s41467-020-18933-4

https://www.frontiersin.org/articles/10.3389/fcimb.2021.717104/full

https://epag.springeropen.com/articles/10.1186/s43054-021-00056-0

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0250196

– so this new study further confirms that this is possible but relatively rare – around 2-6% of pregnancies where the mother has COVID-19 and delivers a newborn who tests SARS-COV-2 positive. Fortunately, the newborn babies themselves are rarely severely affected.

“The main risk in pregnancy is similar with any respiratory infection or any more systemic infection involving the respiratory tract  (including chickenpox, measles, influenza) during the last trimester – where the enlarging foetus splints the diaphragm, preventing the mother from coughing properly to clear any respiratory mucous/secretions that may become infected with commensal bacteria – leading to a much more severe bacterial pneumonia.”

All our previous output on this subject can be seen at this weblink:

www.sciencemediacentre.org/tag/covid-19

‘COVID-19 and vertical transmission: assessing the expression of ACE2 / TMPRSS2 in the human fetus and placenta to assess the risk of SARS-CoV-2 infection’ by Max Beesley et al  was published in  JOG – An International Journal of Obstetrics & Gynaecology on November 4, 2021.’

Declared interests

Dr Chris Gale: “I lead national surveillance of neonatal SARS-CoV-2 infection in hospital.”

Prof Marion Knight: “I lead national surveillance of hospitalisation with covid-19 in pregnancy.”

None others received.