SARS-CoV-2 does not transmit from mother to child during pregnancy

A new study finds no evidence of vertical transmissions of SARS-CoV-2 from mother to child during pregnancy, but there appears to be limited transplacental transfer of anti-SARS-CoV-2 antibodies to the neonates in utero.

“[The] reduced transplacental transfer of anti–SARS-CoV-2 antibodies may leave neonates at risk for infection,” the researchers pointed out.

“Our finding of compromised mother-to-baby transfer of SARS-CoV-2-specific antibodies in third trimester infections has implications for maternal vaccine administration,” said lead author Dr Andrea Edlow from Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, US.

In the prospective cohort study involving 127 pregnant women, 64 were tested positive for SARS-CoV-2 (mean age 31.6 years), based on nasopharyngeal swab RT-PCR. Among the infected women, 36 percent were asymptomatic and 34 percent had mild disease. [JAMA Netw Open 2020;doi:10.1001/jamanetworkopen.2020.30455]

When analysing for viral load in biofluids, the researchers did not detect any viraemia in maternal or cord blood – indicating no evidence of vertical transmission of SARS-CoV-2 infection from mother to child and no placental infection.

For quantification of SARS-CoV-2 antibodies, one out of 77 neonates analysed showed immunoglobuilin M antibodies to the viral nucleocapsid in their cord blood, although viral RNA was not detected in any placenta. The antibodies, as the authors believed, could be from the mothers as RNA analysis showed none of the infants had been infected.

In fact, when analysing for antibodies among the 37 infected women, anti-nucleocapsid antibodies were present in 70 percent of them and anti–receptor binding domain immunoglobin G was found in 65 percent.

As a control comparison for mother-to-neonate transfer of antibodies, the researchers also measured transfer of anti-influenza antibodies in the mother-neonate pairs. Indeed, transfer of antibodies against SARS-CoV-2 was significantly lower than that of anti-influenza haemagglutinin A antibodies from mothers to neonates (mean cord-to-maternal ratios: 0.72 for anti-receptor binding domain immunoglobin G and 0.74 for anti-nucleocapsid, vs 1.44 for anti-influenza; p<0.001).

As transplacental transfer of antibodies from mothers to neonates is usually highest in the third trimester, Edlow said the significantly limited transfer of SARS-CoV-2 antibodies relative to influenza antibodies was unexpected.

“[The study] highlights that pregnant women are a key population to consider in vaccine rollouts. It also raises questions regarding the optimal timing of vaccine administration to best support maternal and newborn immunity,” said Edlow.

“Although it is not known whether the inefficient transplacental transfer of antibodies observed will also extend to antibodies elicited by future SARS-CoV-2 vaccines, it underscores the susceptibility of infants, particularly since it is unlikely that young infants will be eligible for SARS-CoV-2 vaccination,” wrote Drs Denise Jamieson and Sonja Rasmussen from Emory University School of Medicine in Atlanta, Georgia and University of Florida College of Medicine, Gainesville, Florida, US, in a linked commentary. [JAMA Netw Open 2020;doi:10.1001/jamanetworkopen.2020.30564]