A group of researchers in France say they have determined the first clear case of a newborn infected with COVID-19 through its mother’s placenta, according to a case study published on Tuesday.

The study, published in Nature Communications, tracks the birth of a boy in a Paris hospital in March by cesarean section, after his mother was brought to the hospital with symptoms of COVID-19 in the days before his birth. Extensive blood testing of both the mother, the newborn, placenta, and amniotic fluid revealed the baby had contracted COVID-19 through the mother’s placenta, the researchers said.

The newborn was placed in immediate isolation, but within days of the birth, he began to exhibit distress and muscle spasms characteristic with a neurological injury, which the doctors attributed to the virus. Shortly afterward, the newborn’s health began to improve, and both the mother and baby subsequently recovered and were discharged from the hospital.

The case adds to the growing medical debate over whether newborns, plus expectant mothers and fetuses, face an elevated risk of coronavirus infection. On Tuesday, an NIH study said placental transmission of COVID is a rarity, casting further confusion on the extent of the medical risk to expectant mothers and their offspring.

While other case studies have tracked babies born with COVID-19, it hasn’t been clear exactly how newborns contracted the virus—whether it was a prenatal infection, or through the labor, or after the birth. An early study in February in The Lancet, which tracked the birth of nine babies to COVID-19 positive mothers in Wuhan, found no evidence that COVID-19 could be passed to the baby in the womb.

Researchers polled by the Science Media Centre on the study noted that there is still no evidence that COVID-19 represents a heightened risk factor to newborns, and added that this baby’s symptoms could have been attributed to other factors.

“It is unclear whether any of the subsequent symptoms and signs observed in the baby were due to SARS-CoV-2 infection, or due to events that occurred around the time of his birth,” said Marian Knight, professor of child and maternal health at the University of Oxford and head of national surveillance on pregnancy and COVID-19 in the U.K.

“Among the many thousands of babies born to mothers with SARS-CoV-2 infection, a very few have been reported to also have a positive test for SARS-CoV-2—around 1–2%. As in this report, most babies do not appear to become severely unwell,” she noted.

“There isn’t any evidence that the virus is dangerous for babies, though we cannot exclude the possibility that it can cause fetal or neonatal infection that can be associated with really rare conditions as have been reported in children and adults with COVID-19,” said Christoph Lees, professor of obstetrics at Imperial College London.

“To put it another way, the great majority of women who test positive for SARS-CoV-2 or indeed have COVID-19 have normal pregnancy outcomes with healthy babies.”

The CDC currently says that transmission to newborn babies is thought to occur largely through respiratory droplets from mothers or other caregivers immediately after the birth.

It adds that while young babies may be at greater risk from COVID-19 than children older than a year, case studies are limited, and common symptoms are difficult to attribute conclusively to the virus.