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Covid-19 during pregnancy alters fetus immune system, study finds



The immune system of a fetus is altered as a result of maternal Covid-19 infection during pregnancy, according to the latest findings.

Researchers at King’s College London examined the effects of SARS-CoV-2 exposure at various stages of pregnancy. Maternal Covid-19 infection was shown to impact the developing immune system of the fetus without the baby becoming infected with the virus. The results were published in Nature Immunology

The researchers also found that infected mothers transferred passive immunity to their unborn babies. Antibodies against Covid-19 infection were passed through the placenta and this was particularly evident when the mother was infected earlier in the pregnancy. 

Blood samples, which included maternal peripheral blood and neonatal cord blood, were collected from 30 mothers and babies at the time of birth who were attending the maternity unit at Guy’s and St Thomas’ NHS Foundation Trust (GSTT) between May 2020 and March 2021. 

In 16 of these samples, the mother tested positive for Covid-19 up to 14 days before or during the birth. The remaining 14 samples were from mothers and babies where the mother had tested positive for Covid-19 earlier in the pregnancy. An additional 15 neonatal cord blood samples were examined from babies born before the Covid-19 pandemic (pre- January 2020), and the immune status of the samples was compared.

The researchers found that babies born to mothers with very recent or ongoing Covid-19 infections at the time of birth had increased levels of circulating mediators, compounds released into the blood during disease infection. These babies also displayed higher levels of cells involved in rapid infection response in their blood, such as regulatory T cells and natural killer cells. 

Dr Deena Gibbons, a senior lecturer in immunology at King’s College and co-author of the paper, said: ‘This data highlights that the neonatal immune system can be affected by maternal state even in the absence of direct infection of the baby.’

The ability of the immune cells to make mediators was increased in all babies, even when the mother had been infected with Covid-19 in early pregnancy. The researchers intend to investigate whether the immune changes allow the neonate to respond better to subsequent infections after birth. 

Dr Gibbons added: ‘This opens up many avenues of research and suggests that other maternal factors may be capable of changing fetal immune system development.’