An experimental mRNA vaccine by US-drug maker Moderna has shown promise against human cytomegalovirus (CMV) — a common virus that can infect babies during pregnancy.

While the virus rarely causes serious illness in healthy adults, it can cause birth defects and brain damage in newborns infected in utero and deadly infections in immune-compromised adults.

Though healthy adults are largely asymptomatic, one in every 200 newborns worldwide is infected with CMV during the mother’s pregnancy.

“It is the most common congenital infection worldwide,” said Dr. Sallie Permar, the chair of the Department of Pediatrics and Nancy C. Paduano, Professor in Pediatrics at Weill Cornell Medicine.

The study, published in The Journal of Infectious Diseases, provided evidence that the new mRNA vaccine candidate may protect adults against CMV.

Thus, it could potentially prevent women from passing the harmful infection to their babies during pregnancy.

The new mRNA vaccine-elicited responses that were better at preventing the CMV virus from infecting epithelial cells that line the mouth and nose and provide the first line of defence against viral infection, compared with a previously moderately successful vaccine candidate called gB/MF59, from Sanofi and Novartis, revealed the study by the team at Weill Cornell Medicine of Cornell University.

The mRNA vaccine was also more effective at triggering the immune system to destroy CMV-infected cells.

“We learned that the newer vaccine has the potential to be more effective than a previous CMV vaccine candidate because some of the functional immune responses it elicits are higher in magnitude,” Permar said.

The team used the data and patient samples from the gB/MF59 phase 2 trial in adolescent girls as a benchmark to assess the new mRNA-based vaccine.

Moderna used mRNA technology for the CMV vaccine and added a second target — a five-unit protein complex that allows the virus to infect the epithelial cells that line the nose and mouth — in addition to glycoprotein B used by Sanofi and Novartis.

In the study, Permar and her team compared the immune responses of individuals vaccinated with gB/MF59 in the phase 2 trial with those immunised with Moderna’s mRNA-based CMV vaccine in a phase 1 clinical trial that ended in 2020.

Specifically, the team compared the immune responses in people who were protected against CMV infection after receiving the older vaccine.

The Moderna vaccine has moved on to the first-ever phase 3 clinical study for a CMV vaccine candidate, which will help determine if these differences in immune responses will lead to stronger protection against CMV.

“After more than 50 years of research, we are closer than ever to having a licensed CMV vaccine,” Permar said.

“The new mRNA platform has a lot of potential.”