Varicella, commonly known as chickenpox, is a highly contagious disease caused by the Varicella-Zoster Virus (VZV). While often considered a mild childhood illness, it poses significant risks for infants. A baby can contract chickenpox, but the severity and likelihood of infection are heavily influenced by the mother’s immunity status and the infant’s age.
Passive Immunity from the Mother
A newborn baby often possesses a temporary shield against VZV through a process called passive immunity. This protection is established when the mother’s antibodies are transferred to the fetus across the placenta during the later stages of pregnancy. Specifically, Immunoglobulin G (IgG) antibodies provide this temporary defense.
For this transfer to occur, the mother must have a history of VZV infection or vaccination, meaning her immune system has already developed the protective IgG antibodies. These antibodies circulate in the infant’s bloodstream at birth, offering a protective effect against the virus. The mother’s immune status is thus the primary factor determining the newborn’s initial protection.
This maternal immunity is not permanent and begins to wane rapidly as the infant’s body breaks down the transferred IgG antibodies over time. A significant portion of infants become susceptible to VZV infection as early as three months of age. Most babies lose all meaningful passive protection by six months, leaving them vulnerable until they are old enough to receive their own vaccine.
Infants born to mothers who never had chickenpox or were never immunized against VZV do not receive this initial protective transfer. Consequently, these babies are fully susceptible to the virus from the moment they are born. This lack of initial defense means they face a higher risk of severe disease if exposed during the first few months of life.
How Chickenpox Presents in Infants
When an unprotected infant contracts VZV, the illness often starts with general signs like fever, fussiness, and a reduced appetite. Within a day or two, the characteristic rash begins to appear, typically starting on the face, chest, or back before spreading across the body. The rash progresses quickly through stages, starting as small red spots that turn into itchy, fluid-filled blisters, which eventually crust over.
The rash is described as “pleomorphic,” meaning lesions in different stages—spots, fresh blisters, and scabs—can all be seen at the same time. The infection in an infant can be more serious than in an older child, especially for those under one year old who lack maternal antibodies. This increased severity is due to their still-developing immune system, which struggles to contain the virus effectively.
Serious complications are a concern for non-immune infants, including the risk of disseminated disease where the virus spreads beyond the skin. Potential complications include bacterial infections of the skin, or more dangerous systemic issues. Infants face a risk of primary VZV pneumonia and inflammation of the brain, known as encephalitis, which carry high mortality rates.
These complications require immediate medical attention, particularly if the infant exhibits a high or persistent fever, lethargy, or signs of dehydration. Very young infants, especially those under one month of age, are considered at the highest risk for severe or life-threatening outcomes.
High-Risk Scenarios and Prevention Strategies
Specific timing of VZV exposure presents unique, high-risk scenarios for the newborn. One of the most dangerous situations is Neonatal Varicella, which occurs when a mother contracts chickenpox shortly before or after delivery. The highest risk window is when the mother’s rash appears from five days before to two days after birth.
In this narrow timeframe, the mother transmits the virus but has not yet transferred sufficient protective IgG antibodies to the baby. The infant receives a high viral load without passive immune defense, leading to a severe, disseminated infection with a significant mortality rate, sometimes reported up to 30%.
A separate, though rare, risk is Congenital Varicella Syndrome, which occurs if the mother contracts the virus early in pregnancy, typically before 20 weeks gestation. This can result in birth defects like limb abnormalities, eye problems, or neurological damage.
Since the standard Varicella vaccine is not given until 12 to 15 months of age, prevention focuses on protecting the vulnerable infant until then. This strategy is known as “cocooning,” which involves ensuring all close household contacts and caregivers are immune to VZV through prior infection or vaccination.
By vaccinating those who interact with the baby, the risk of bringing the virus into the home and exposing the infant is drastically reduced. In cases of known high-risk exposure, such as a mother contracting VZV around delivery, Varicella-Zoster Immune Globulin (VZIG) may be administered to the infant to provide immediate, temporary immunity.