Cytomegalovirus, or CMV, is a common infection in both adults and children. Clinical trials for several vaccines are currently underway to help prevent people from developing CMV.

The Centers for Disease Control and Prevention (CDC) estimates that nearly 1 in 3 children in the United States will contract CMV before 5 years of age, and over half of adults will acquire the infection by age 40.

“One of the aspects of CMV that makes it so insidious is the fact that most infections are asymptomatic in otherwise healthy individuals,” said Mark R. Schleiss, MD, a professor of pediatrics at the University of Minnesota.

This is because, for most people, a healthy immune system will suppress the virus so it cannot replicate and cause illness and, therefore, symptoms.

CMV belongs to the same family of viruses as chickenpox, herpes simplex, and mononucleosis. Just like other herpes viruses, CMV can establish latency after initial infection. This means the virus goes dormant but remains in the body’s blood cells, establishing a lifelong infection.

If the immune system becomes weakened at any point — due to illness, medication, or surgery — the virus can reactivate, potentially leading to severe illness. Illness due to CMV infection can be a serious cause of complications for individuals undergoing transplants or in people living with HIV — in some cases, it can even be fatal.

Infection with CMV can also be serious if it occurs during pregnancy since the virus can pass to the fetus. In this case, CMV can cause a wide range of permanent disabilities, including:

  • hearing loss
  • cognitive issues
  • seizure disorders

Current treatment of CMV involves the use of antivirals to help control the replication of the virus. However, new research aims to prevent serious complications from CMV by stopping the infection before it happens. This article explores the current state of CMV vaccine research and its progress to date.

Learn more about CMV.

Research into a CMV vaccine has progressed in recent years.

A brief history

Currently, no vaccine prevents CMV infection or illness, though not for lack of trying. Scientists developed the first attempt at a CMV vaccine more than 50 years ago, with limited success.

“There have been lots of studies [over the years], often in immunocompromised patients — who [aren’t ideal] subjects for a vaccine trial because they don’t respond well immunologically to vaccines,” explained Dr. Schleiss. “On the other hand, they get really sick with CMV, so it becomes a good population to study for ‘proof of concept.’”

Dr. Schleiss also said that early studies of CMV vaccine candidates used attenuated, or weakened, forms of the virus. These vaccines were unsuccessful in preventing either infection or serious illness in high-risk individuals.

Ongoing research

As molecular techniques improved, better vaccine candidates have emerged. These new vaccines aim to prevent serious complications from CMV infection via one of two strategies:

  • a therapeutic vaccine to prevent illness in transplant recipients or other people who are immunocompromised who have already acquired CMV
  • a preventive vaccine to help avoid CMV infection during pregnancy

Several vaccines are currently in clinical trials to help achieve these goals. Most of these studies are working toward the first goal — preventing illness in people who are immunocompromised — and are in the earlier stages of development and testing.

The only CMV vaccine candidate to reach a phase 3 clinical trial — the final stage of testing before being submitted for approval — is a vaccine intended for use in young, healthy females of reproductive age. It uses the same mRNA-based technology as the two major COVID-19 vaccines.

“The goal of CMV vaccination [in this study] is to prevent congenital CMV infection by preventing infection in the mother,” explained Dr. Schleiss, an investigator in the study. “If she’s never infected with the virus, she can’t transmit it to the baby.”

While this trial is still in progress and results are not yet available, Dr. Schleiss is cautiously optimistic. He explains the issue with many other vaccine candidates in the past has been the high bar required by pharmaceutical companies to define success.

“[Preventing infection] sounds simple, but it is not that simple because there are actually very few vaccines that prevent infection,” he said. “Usually, the best a vaccine can do is prevent disease. COVID vaccines were a great example.”

“Natural, long-term CMV infection does not protect a woman from reinfection later, with a new ‘strain’ of CMV, and reinfections can lead to transmission and disability even in naturally immune women,” he explained. “Hence, you need a vaccine that is better than natural immunity. Tough task, but may be possible with the mRNA vaccines because they are so highly immunogenic.”

Until a vaccine is available, people can take steps to help prevent CMV infection if they are concerned about potential complications.

“It’s a hard virus to ‘catch’ and requires intimate contact,” said Dr. Schleiss. “Kissing and sexual intercourse can lead to transmission.”

“Other sources of saliva and body fluids, especially urine, are risky,” he added. “Hence, young [parents] exposed to these body fluids from their toddlers and young children are at risk, especially if their toddler attends group day care, where the risk of acquisition of CMV from another child is high.”

“For this reason, some experts have said that we should not use a CMV vaccine to immunize young women, but rather that we should use a CMV vaccine to immunize toddlers in group day care,” he noted. “If they don’t ‘catch’ CMV after vaccination, then they can’t take it home to their mom.”

Dr. Schleiss recommends regular handwashing and other protective measures to help avoid exposure, especially if a person is at risk for severe complications from infection.

He also notes that many babies who acquire CMV before or shortly after birth will not develop any complications but suggests that a proactive approach to prevention is still the best way to help avoid serious health concerns.

A healthy immune system will help prevent illness from CMV infection in most people. However, for some individuals, infection with CMV can lead to serious complications. These include severe illness in those who are immunocompromised, or congenital complications in newborns following transmission from parent to child during or after pregnancy.

Research into a vaccine for CMV has progressed in recent years, and several new vaccine candidates are currently under study in clinical trials. However, until a vaccine becomes available, regular handwashing and avoiding potential exposure through body fluids can help prevent infection and potential complications from the virus.