COVID-19 virus not retained in placenta after maternal recovery

A new Yale study published in JAMA Network Open finds that the virus that causes COVID-19 does not linger in placental tissue weeks to months after a pregnant woman recovers from infection - offering important reassurance for clinicians and patients alike.

Key findings:

• No persistent virus detected: Using sensitive laboratory techniques, researchers found no SARS-CoV-2 RNA or protein in placentas collected 40 to 212 days after maternal infection - including in pregnancies that ended in stillbirth.
• The placenta clears the virus: Results indicate the placenta does not serve as a long-term reservoir for SARS-CoV-2 after recovery.
• But damage may remain: Some placentas showed structural and inflammatory changes resembling those seen in acute COVID-19 placentitis, suggesting the immune response can leave lasting marks even after the virus is gone.

Early in the pandemic, Yale researchers demonstrated that SARS-CoV-2 could infect the placenta during acute maternal illness - a condition known as COVID-19 placentitis that was linked in some cases to inflammation and pregnancy complications. The new study tackles a critical follow-up question: Does the virus remain in placental tissue after the mother recovers?

Our earlier work showed that SARS-CoV-2 can infect the placenta during acute COVID-19. In this study, we wanted to know whether the virus might linger in the placenta long after a woman recovers from infection. We found that it does not."

Shelli F. Farhadian, associate professor of medicine (infectious diseases) at Yale School of Medicine (YSM), associate professor of epidemiology at the Yale School of Public Health, and co-author of the study

To investigate, researchers analyzed placentas collected at delivery from women who had recovered from COVID-19 40 to 212 days earlier, spanning pregnancies that ended in stillbirth and those resulting in healthy births. Using sensitive techniques to detect viral protein and RNA, the team found no evidence of persistent virus in any of the samples - even in cases of fetal or neonatal loss.

However, investigators did observe structural and inflammatory changes in some placentas, suggesting the immune response triggered during infection can outlast the virus itself.

"These results indicate that the placenta is effective at clearing the virus after maternal recovery," said Harvey J. Kliman, director of the Reproductive and Placental Research Unit at YSM and senior author of the study. "But the structural changes we observed suggest that the damage incurred during infection may persist."

The researchers note that the study is limited by its small sample size and retrospective design, and that additional research is needed to determine how often placental injury occurs following maternal SARS-CoV-2 infection.

The research was supported by the National Institutes of Health.