The baby was born early by Caesarean section because of concerns about his heart rate racing prior to birth, which may have been caused because his mother had a high fever caused by Covid-19.
The mother was discharged six days after the birth, but the baby was transferred to intensive care. Scans later showed that there was similar inflammation in the brain to that usually seen in adults.
The baby was discharged after 18 days, and doctors said his brain had started to recover after two months of follow-up.
Commenting on the report, Christoph Lees, professor of obstetrics at Imperial College London, said: “This is the most convincing case yet reported of transplacental transmission.
“We now have data from several thousand of pregnancies where mothers had the virus. In some cases, the babies are likely to have caught the infection either transplacentally, in the process of labour/delivery or afterwards.
“The great majority of women who test positive for SARS-CoV-2, or indeed have Covid-19, have normal pregnancy outcomes with healthy babies.”
There have been 244 live born babies of mothers infected with coronavirus in Britain, and 95 per cent showed no sign of the virus.
Marian Knight, professor of maternal and child population health at the University of Oxford, said: “The most important message for pregnant women remains to avoid infection through paying attention to hand-washing and social distancing measures.”