CMV is a common virus that can cause complications in pregnant people and people with a repressed immune system. Several CMV vaccines are in development.

Cytomegalovirus (CMV) is one of the most common viruses that causes infections in humans, but most people have never heard of it.

In the United States, it’s estimated that nearly 1 in 3 children have contracted CMV by the time they turn 5 years old. By the time adults reach 40, over half have contracted the virus.

Despite how common CMV is, survey results from the National CMV Foundation found that less than 10% of people have heard of this virus, including people who are at risk for developing serious complications from CMV infection.

In this article, we take a closer look at what happens during a CMV infection, who is affected, and the progress that’s being made in the development of vaccines to prevent complications linked to CMV infection.

CMV is a common virus that many people are exposed to throughout their life. Most infections happen in early childhood, but adults and adolescents can be infected, too, especially if they have frequent, close contact with young children. The virus is typically spread through contact with infected body fluids, such as saliva, urine, or blood.

Once someone has developed a CMV infection, the virus stays in their body for life. Typically, the virus remains inactive but can still be found in long-lived blood cells and can reactivate in some circumstances.

In most people, CMV infection is asymptomatic, meaning they don’t show symptoms.

“Whether it’s a toddler in group day care, or a school-aged child, or a sexually active young adult, a primary CMV infection usually produces no illness,” explained Mark Schleiss, professor of pediatrics at the University of Minnesota. “Thus, there is little public knowledge or understanding of CMV. Indeed, why should anyone care about a virus that doesn’t even make you sick?”

The problem, Schleiss says, is that CMV can cause severe complications in some cases. For most people, their immune system keeps the virus under control so that it can’t replicate or cause illness. But for people whose immune system is repressed — either due to illness or certain medications — the virus can cause serious health problems.

In these cases, CMV infection can cause severe symptoms affecting these areas of the body:

  • eyes
  • lungs
  • liver
  • digestive tract

Infection with CMV can also have serious consequences if it happens during pregnancy. “Even if there are no symptoms, CMV infection acquired during pregnancy — especially if it’s the first lifetime CMV infection for that pregnant person — can, if passed to the developing fetus, cause a wide range of permanent disabilities.”

These include:

  • hearing or vision loss
  • developmental disabilities
  • growth problems
  • seizure disorders
  • lung, spleen, or liver problems

An estimated 1 in 200 infants in the United States are born with CMV, known as a congenital CMV infection. Of these infants, about 20% will develop serious, long-term health problems.

Because of the potential for severe complications in these groups, researchers are working to develop CMV vaccines that either prevent illness in immunocompromised people who’ve already contracted CMV or prevent CMV infection during pregnancy.

There’s currently no vaccine available for the prevention of CMV infection or illness. Several candidates have been studied over the years, but none have been able to provide meaningful benefits for at-risk groups.

As vaccine technologies have improved in recent years, though, many new vaccine candidates have emerged. Several new vaccines are currently being studied in clinical trials, including potential vaccines for both immunocompromised people and the prevention of congenital CMV.

Schleiss is currently involved in a clinical trial studying a CMV vaccine for use in people of child-bearing age. He explains that the goal of vaccination in this trial is to prevent CMV infection in people who may become pregnant. “If [they’ve] never been infected with the virus, [they] can’t transmit it to the baby,” he said.

Results from this trial — and others that are ongoing — are not available yet. But with advances in how vaccines are developed, Schleiss is optimistic about the possibility of a CMV vaccine in the future.

While a vaccine is not yet available, there are steps you can take to prevent CMV infection. “CMV is hard to ‘catch’ and easy to ‘kill,’” said Schleiss. “Good handwashing destroys the virus easily.”

Results from a 2009 study suggested that counseling on how to take basic preventive steps like handwashing can help prevent infection with CMV in pregnant people.

The problem is, as Schleiss explained, that many people don’t know about CMV and the potential risks.

“Virtually always, I see a baby with CMV at birth, and the baby’s [parent] tells me [they] never, ever heard of CMV — until the virus infected [them] and [their] baby,” he said.

“Until a vaccine is licensed, prevention is our best hope. A lot of congenital CMV infections could be prevented if moms only knew about it and how to prevent it.”

Most people who contract CMV won’t experience any kind of illness, but this isn’t the case for everyone. Certain groups, including immunocompromised or pregnant people, are at risk for serious complications from infection. However, despite these risks, many people aren’t aware of CMV or its possible effects.

CMV vaccine research has made progress in recent years, and several vaccine candidates are currently in clinical trials. Until a vaccine is available, many CMV infections can be prevented with regular handwashing and avoidance of potential exposures.

If you have concerns about serious complications for you or your child, a healthcare professional can help you better understand the risks of CMV and take steps to minimize the likelihood of infection or illness.