Cytomegalovirus (CMV): The Disease and Vaccine

Cytomegalovirus (CMV): The Disease and Vaccine

Many people may not have heard of a virus called cytomegalovirus or CMV, but many have suffered from a CMV infection. CMV is most concerning because it can cause birth defects when a woman is infected during pregnancy. In the U.S., CMV is the most common infection to cause birth defects (known as congenital CMV). When an infection passes from the woman to her developing baby during pregnancy, the baby can be infected. 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) is a viral infection that is spread from person to person. CMV is spread through direct contact with body fluids including urine, saliva, blood, tears, semen and breast milk. The virus can also be transmitted through transplanted organs and blood transfusions.

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 months after their infection, positioning them to spread the virus to others even if they don’t have symptoms. People who are often around young children are more likely to become infected with CMV because of the lingering quantities of virus in a child’s saliva and urine. More than half of adults over 40 years of age have been infected by CMV.

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 hepatitis (inflammation of the liver).

Some people are at higher risk for 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
  • Encephalitis (inflammation of the brain and spinal cord)

While pregnancy increases a person’s risk for severe CMV, many pregnant women do not experience symptoms and, therefore, don’t 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
  • Jaundice (yellowing of skin or whites of the eyes)
  • Microcephaly (small head)
  • Enlarged liver and spleen
  • Seizures
  • Damaged eye retina

Complications of congenital CMV can include hearing loss, cerebral palsy, developmental delays, vision loss, seizures, and death.

The vaccine

Currently no approved CMV vaccines are available in the U.S.; however, an mRNA vaccine is being tested and will hopefully be approved in the near future. The clinical trials are in women of childbearing age and are evaluating whether the vaccine is safe and induces a sufficient immune response against CMV. Ideally, a CMV vaccine would be given to people before they become pregnant to prevent infection during pregnancy, thereby preventing congenital CMV. This is the same strategy that is used to prevent rubella (German measles) infection, another cause of congenital birth defects. 

How is the CMV vaccine made?

The CMV vaccine closest to approval is an mRNA vaccine. The mRNA vaccine contains the code, or blueprint, for several CMV proteins located on the surface of the virus. After getting the shot, the vaccinated person’s cells will make the CMV surface proteins, causing the person’s immune system to make a protective immune response against the virus. Because the mRNA vaccine only provides the code for a few CMV proteins, not the entire virus, the vaccine cannot cause CMV disease (see How Are Vaccines Made?). 

Does the CMV vaccine work?

The mRNA vaccine is still being tested, but in studies to date, the vaccine has been shown to induce an immune response. Results have not identified any concerns related to serious adverse events. The data also suggest that immune responses against CMV last for at least three years after vaccination. Even if this vaccine is approved for use in the U.S., studies will continue. As such, we will learn more about how long immunity lasts and continue monitoring for any safety concerns that may not have been identified during clinical trials.

Does the CMV vaccine have side effects?

Results from early trials indicate the people who receive the vaccine may experience mild side effects, such as pain or soreness where the shot was given. A few people who received the vaccine also experienced headache, fatigue, muscle pain and chills. Studies will continue to monitor for side effects even if the vaccine is approved for use. Sometimes, rare side effects of vaccines are only identified after millions of doses of vaccine have been administered. 

Other questions you might have

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

While you cannot completely 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. 

I am at high-risk for CMV. Will the vaccine be available for anyone other than for CMV prevention during pregnancy? 

Currently, the mRNA vaccine is only being studied in women in their childbearing years. Vaccines aimed at preventing CMV in other high-risk populations, including transplant recipients, are under development. 

Relative risks and benefits

Do the benefits of the CMV vaccine outweigh the risks?

CMV is a common viral infection with over half of U.S. adults becoming infected by the time they are 40 years of age. 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. 

CMV during pregnancy (i.e., congenital CMV) can cause the developing baby to be infected. Congenital CMV is the leading infectious cause of birth defects in the U.S. Babies born with congenital CMV may experience long-term complications, including hearing loss, microcephaly (small head) and developmental and motor delays. 

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
  • Encephalitis (inflammation of the brain and spinal cord)

Congenital CMV

  • Rash
  • Jaundice (yellowing of skin or whites of the eyes)
  • Hearing loss
  • Microcephaly (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 Aug. 6, 2025