The virus that causes COVID-19 does not appear to linger in placental tissue after a pregnant patient recovers from acute infection, according to a small case-control study published this week in JAMA Network Open. The findings suggest that placental infection is unlikely in the weeks and months after illness, even in cases with adverse outcomes.
“Our motivation for doing the study was to see if there was 'long COVID' in the placenta,” Harvey J. Kliman, MD, PhD, director of the Reproductive and Placental Research Unit at Yale School of Medicine and senior study author, told CIDRAP news in an email. “This is one of the scariest aspects of COVID: long COVID leading to chronic brain issues.”
“We just didn’t know if this could also happen in the placenta, which is a magnet for the SARS-CoV-2 virus (because the placenta is covered with ACE2 [angiotensin-converting enzyme 2], the receptor for the spike protein of the virus),” he added. “So we thought it was necessary to look at this issue.”
No trace of virus weeks after infection
For the study, the Yale University team analyzed 12 placentas collected at delivery from October 2020 to December 2024 to compare three groups of placentas: a pre-pandemic control (one placenta); active cases of acute COVID-19 placentitis (inflammation of the placenta; four); and pregnancies following maternal recovery from infection (seven).
Of the seven placentas from women who had recovered from SARS-CoV-2 infection, collected 40 to 212 days after infection, three resulted in stillbirth, and four resulted in healthy full-term babies. As early as 40 days after maternal infection, no trace of the virus or its genetic material was found in any of the placentas from women who had recovered from COVID, even in areas of the placenta with inflammatory lesions.
“Our earlier work showed that SARS-CoV-2 can infect the placenta during acute COVID-19,” first author Shelli F. Farhadian, MD, PhD, said in a Yale news release. “We found that it does not.” The absence of detectable virus in these placentas suggests that adverse outcomes occurring after maternal recovery are not driven by ongoing infection.
At the same time, the researchers did observe structural and inflammatory changes in some of the placentas from women who had recovered from acute infection, suggesting that the body’s immune response to the infection can linger even after the virus has been cleared.
Placental damage seen during infection, not after recovery
Among the four placentas collected from women with active COVID infections, the virus could be seen clearly in placental cells, and the placentas showed typical signs of virus-related damage. Of those pregnancies, three ended in stillbirth and one in neonatal loss.
The study had several limitations. The sample size was small, and the retrospective design limited the ability to estimate how often viral persistence in placental tissue might occur across different populations or vaccination statuses.
Even so, says Kliman, “Our study reassures pregnant patients that if they become infected with COVID during their pregnancy, their baby’s placenta can also become infected, but in a matter of weeks to at most a month or two, can clear the virus out of the placenta.
“This means that the placenta won’t become a reservoir for the virus, persistently reinfecting them or their baby.”
