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Cytomegalovirus, or CMV, is a very common virus. Most people catch it, have no symptoms, and carry it quietly for life. It matters in two situations: in pregnancy, when it can pass to a baby, and in people whose immune system is weakened.
CMV belongs to the herpes family. In healthy children and adults it usually causes nothing, or a mild illness with fever, sore throat and tiredness. It is not rare or exotic, and catching it is not a sign anyone did anything wrong.
It is not harmless in every situation. When CMV crosses the placenta, the baby has congenital CMV. Most of those babies are well: Canada’s Drug Agency reports 85% to 90% have no symptoms at birth, and 10% to 15% of them later develop effects, usually hearing loss.
The same infection can look completely different in two people.
Some risk factors cannot be changed:
Others can often be worked on, usually with support from a health care team. The Canadian Paediatric Society describes these measures in pregnancy:
In a newborn, congenital CMV is confirmed by testing urine or saliva before 21 days of age, using PCR or rapid viral culture. After three weeks a positive result can no longer be separated from an infection caught after birth, so the window is short. Babies with confirmed infection have hearing and eye assessments, blood tests and sometimes brain imaging, with hearing rechecked over time. In pregnancy CMV is assessed with blood tests and, in specialist care, amniotic fluid testing.
Healthy children and adults with mild CMV illness need no treatment. Where it is used, a health care team may discuss:
What suits one child will not suit another. These are decisions for you and your own clinician.
There is no CMV vaccine authorised anywhere. The largest attempt so far, an mRNA candidate tested in CMV-negative women aged 16 to 40, did not meet its phase 3 primary endpoint, and the sponsor discontinued that programme in October 2025. Canada’s Drug Agency also found both universal and targeted newborn screening in use in different provinces, with no national standard, and it is not established which babies without symptoms at birth benefit from antiviral treatment.
Taking part is voluntary. You give informed consent first, and you can stop at any time without affecting the care you get from your own clinicians. No one can say in advance whether a study will help you or your child.
This page is written in plain language for people considering clinical research. It is general health information, not medical advice, and it does not replace a conversation with your own doctor or nurse practitioner.
Most babies are not. The Canadian Paediatric Society reports that congenital CMV affects 0.5% to 1% of live births in North America and Europe, and that only about 10% of infected newborns show clinical features at birth. Among the 85% to 90% who have no symptoms at birth, Canada's Drug Agency reports that 10% to 15% later develop long-term effects, most often hearing loss. So the great majority of babies with congenital CMV grow up without lasting problems, while a minority need close follow-up. Nothing you did or did not do caused the infection: CMV is an extremely common virus that most adults have already had.
It depends where you live. Canada's Drug Agency reports that Alberta, Saskatchewan, Manitoba and Ontario have or are implementing universal newborn screening for congenital CMV, while British Columbia, New Brunswick and Nova Scotia have province-wide targeted screening, usually triggered by a failed hearing screen or another risk factor. Programmes are changing, so your midwife, nurse or paediatrician is the best source for what happens where your baby is born. Testing needs to be done on urine or saliva before 21 days of age to confirm the infection was congenital.
The Canadian Paediatric Society describes avoiding contact with the saliva and urine of young children: not sharing toothbrushes, pacifiers, food, drinks or utensils with a toddler, kissing a young child on the head or cheek rather than the mouth, washing hands after nappy changes and after wiping noses, and cleaning toys and high-touch surfaces regularly. These are described as reasonable precautions rather than guarantees, and CMV is common enough that many people are exposed without knowing.
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