Discussion
Despite very few reported cases of neonatal COVID-19, it is an ongoing discussion whether SARS-CoV-2 can be vertically transmitted from the mother to the child during labor. As symptomatic women with COVID-19 have often been delivered by caesarean section it is still difficult to evaluate whether vertical transmission is harmless or constitutes a potential threat to the newborn which could be prevented by delivery by caesarean section (1). Previously, three cohort studies with a total of 76 women, have reported three cases where SARS-CoV-2 was detected in vaginal swabs (4–6), where only one of the three women was pregnant.
We present a single case of a pregnant woman who was clinically affected by COVID-19 in week 26 gestation, where SARS-CoV-2 was also detected in two vaginal swabs. This case raises concern that SARS-CoV-2 could be vertically transmitted during labor, however the clinical implications of the findings should be discussed.
The cycle threshold values were markedly higher for the vaginal swabs than for the pharyngeal swabs, indicating that there was a lower presence of viral DNA. A week after the symptoms had resolved, SARS-CoV-2 could still be detected in a pharyngeal swab but not in vaginal swabs. This might imply that intrapartum transmission is most likely when the mother is symptomatic, and the infant is not yet protected by maternal antibodies.
In the present case, there are several potential sources for the viral presence in the vagina. Theoretically, the vaginal epithelium is not abundant in angiotensin-converting enzyme 2 (ACE2) receptors, but they are upregulated during pregnancy (2). Hence, viral replication in the vaginal epithelium itself is possible as the coronavirus binds to their target cells though the ACE2 receptors. Further, as the patient was being treated with anticoagulants at the time and had a history of vaginal bleeding during pregnancy, it is possible that viral RNA was being exudated from the blood stream, instead of actually being released by the vaginal epithelium itself. There is also potential of seminal contamination (3), however the patient had had coitus three to four days before the vaginal swab and her partner first tested positive a couple of days after the patient experienced the first symptoms.
Despite the risk of vertical transmission of COVID-19 during labor presumably being low (7,8) and with infants being very likely to have a mild course of the disease should they become infected (1), we recommend all women testing positive for SARS-CoV-2 in pharyngeal swabs to be routinely tested with a vaginal swab to gain more knowledge regarding presence and level of the viral load in both symptomatic and asymptomatic women with active COVID-19 infection. We also suggest that mode of delivery should be discussed with women at risk of going into labor with a recently discovered COVID-19 infection, where passive immunity of the baby is unlikely, especially in more severe cases, where caesarean section may be preferable due to potentially higher viral load in the vagina.