Cytomegalovirus (CMV): The Disease & Vaccine

Cytomegalovirus (CMV): The Disease & Vaccine

It’s the 1980s and you’re a pregnant healthcare worker who cares for newborns. When a baby in your care is found to have a condition called congenital CMV, you are told you can no longer care for the infant. The risk to your own baby is too great.

Flashforward to 2026, a pregnant healthcare worker caring for newborns is no longer restricted in this way. Why? Because the virus that causes congenital CMV is so common that your risk for infection from exposure at work is no greater than your risk for exposure in the community. 

This scenario in which healthcare workers are restricted from caring for patients because of their own risk may be something you’ve never considered. You may also have never heard of congenital CMV. Most people haven’t, but many people have been exposed to cytomegalovirus or CMV. CMV is most concerning because it can cause birth defects when a woman is infected during pregnancy. CMV is the most common infection to cause birth defects in the U.S. and around the world. When babies are born with effects from a CMV infection, the condition is called congenital CMV. When CMV passes from the woman to her developing baby during pregnancy, the baby can be infected. In the U.S., about 1 in 200 babies are born with congenital CMV. One in 5 babies with congenital CMV will have birth defects or experience long-term health problems. In severe cases, CMV can cause pregnancy loss.

The disease

What is CMV and how do you catch it?

Cytomegalovirus (CMV) only infects people. It is a member of the herpes virus family. Like other herpes viruses, CMV stays in a person’s body after they are infected, and it can reactivate throughout life. Reactivation can occur when a person’s immune system is compromised. During pregnancy, changing levels of hormones can cause reactivation. However, the greatest risk occurs when a woman is infected for the first time during pregnancy.

CMV is spread from person to person through direct contact with body fluids including urine, saliva, blood, tears, semen and breast milk. The virus can also be spread through transplanted organs and blood transfusions. During pregnancy, it can infect the placenta and spread to the developing baby.

Most people have been exposed to CMV. Studies suggest that in developed countries 4 to 8 of every 10 people have evidence of a previous CMV infection. In developing countries as well as among some groups of people in developed countries, 10 of 10 people have evidence of a past infection.  Many young children become infected in group childcare environments, such as daycare centers. In the U.S., nearly 1 in 3 children are infected by the age of 5. The virus can stay in a child’s saliva and urine for up to two years after their infection. As a result, people who are often around young children, such as pregnant mothers, are more likely to become infected with CMV because of the lingering quantities of virus in a child’s saliva and urine. Even if a child does not have symptoms, they can spread the virus because it is in their saliva and urine.

CMV does not cause serious health problems for most people who become infected. Most healthy adults, children and infants who acquire CMV have very few symptoms and no long-term health complications from the infection. Symptoms may include: 

  • Fever and fatigue
  • Sore throat
  • Swollen glands

Although rare, some otherwise healthy people experience mononucleosis (mono)-like illness with prolonged fever or inflammation of the liver, called hepatitis.

Some people are at higher risk of severe disease or complications. These include babies born early or with low birth weights and people with weakened immune systems. 

People with weakened immune systems include those who have chronic infections, like HIV; are pregnant; or are receiving medications that weaken their immunity. These individuals may experience more severe or even life-threatening symptoms. Symptoms for people with impaired immune systems may include:

  • Fever and fatigue
  • Shortness of breath or cough
  • Blurry vision or loss of vision
  • Stomach pain, blood in stool, nausea, vomiting, diarrhea
  • Inflammation of the brain and spinal cord, called encephalitis

Pregnancy increases a person’s risk for severe CMV, but many pregnant women do not experience symptoms or even know they are infected. If the virus infects the developing baby, the baby can develop congenital CMV. One in 5 babies with congenital CMV will have birth defects or long-term health conditions because of the infection. 

Symptoms of congenital CMV include:

  • Rash
  • Hearing loss
  • Yellowing of skin or whites of the eyes, called jaundice
  • Small head, called microcephaly
  • Enlarged liver and spleen
  • Seizures
  • Damaged eye retina

Complications of congenital CMV can include: 

  • Hearing loss
  • Cerebral palsy
  • Developmental delays
  • Vision loss
  • Seizures
  • Death

The vaccine

Currently, no CMV vaccines are available in the U.S. The goal of vaccination would be to protect women who do not have evidence of a previous CMV infection prior to pregnancy. This is the same strategy that is used to prevent rubella (German measles) infection, another cause of congenital birth defects. When a woman’s first CMV infection occurs during pregnancy, the developing baby’s risk for developing congenital CMV increases dramatically.

Development of an mRNA vaccine that was in phase III clinical trials was stopped in late 2025 because the vaccine did not appreciably decrease the risk of infection during pregnancy. 

Several other candidate vaccines are in clinical trials; however, the trials are in earlier stages than the mRNA vaccine was, and, in some cases, they are being evaluated in other at-risk populations, such as transplant patients.

Other questions you might have

I am pregnant, how can I protect myself and my baby from CMV infection?

While you cannot eliminate your risk of CMV, you can lower your chance of getting CMV and passing it to your baby by reducing your contact with saliva and urine from babies and young children. Try not to share food, utensils, straws or cups with a child and remember to thoroughly wash your hands after changing a diaper or helping a child use the toilet. 

What other groups are at increased risk from CMV infections?

CMV is a common viral infection that does not generally cause severe symptoms. But because this virus remains in the body, it can complicate other conditions. A few considerations are important:

  • First, some groups are at increased risk for CMV infections, including transplant patients and people with HIV.
  • Second, some studies have suggested that evidence of a previous CMV infection may increase the risk for: 
    • Development of some cancers
    • Aging of the immune system, called immunosenescence
    • Progression of diseases, such as heart disease and tuberculosis, and negative outcomes following severe illness requiring intensive care 
  • Finally, some evidence suggests that people with a history of CMV infection may have lower immune responses to routine vaccines, like influenza and COVID-19.

Relative risks and benefits

Do the benefits of the CMV vaccine outweigh the risks?

CMV is a common viral infection with 4 to 8 of every 10 people have evidence of a previous CMV infection. Most people who get CMV experience mild symptoms, but some may develop more severe symptoms or complications. CMV can cause more serious symptoms in infants, pregnant people, and people with weakened immune systems. 

Congenital CMV can cause the developing baby to be infected. Congenital CMV is the leading infectious cause of birth defects in the U.S. and around the world, affecting 1 of every 200 babies born. One in 5 babies with congenital CMV will have birth defects or experience long-term health problems, including hearing loss, small head and developmental and motor delays. In severe cases, CMV can cause pregnancy loss.

Disease risks

  • Fever and fatigue
  • Sore throat
  • Swollen glands
  • Mononucleosis
  • Hepatitis (liver inflammation) 

Possible complications 

  • Shortness of breath or cough
  • Blurry vision or loss of vision
  • Stomach pain, blood in stool, nausea, vomiting, diarrhea
  • Inflammation of the brain and spinal cord

Congenital CMV

  • Rash
  • Yellowing of skin or whites of the eyes
  • Hearing loss
  • Small head
  • Enlarged liver and spleen
  • Seizures
  • Damaged eye retina and vision loss
  • Developmental and motor delay
  • Lack of coordination or weakness
  • Death 

Vaccine risks

No CMV vaccine is currently approved for use in the U.S.

Reference

 

Reviewed by Paul A. Offit, MD, on March 12, 2026