Varicella Zoster Virus AB (IgG) Test

Varicella zoster virus is the virus that causes chickenpox during first infection and shingles when it reactivates later in life. After you are exposed, either through natural infection or vaccination, your immune system produces proteins called antibodies. The IgG type of antibody is the long-lasting form that provides memory. Detecting VZV IgG in your blood means your immune system has already learned to recognize and defend against the virus.

Natural chickenpox infection typically generates stronger and more durable IgG levels than vaccination. That said, vaccination is highly effective at preventing disease. When vaccinated, antibody levels peak about a year later, then gradually decline. This is why two doses are recommended in childhood; they provide higher and more sustained IgG levels than a single dose. In adults, IgG often persists for decades, but the risk of shingles depends not only on antibodies but also on cellular immunity, the part of the immune system that directly attacks infected cells.

Babies are born with some protection because IgG antibodies cross the placenta from mother to child. These maternal antibodies fade by 6 to 12 months of age, which is why vaccination is recommended after infancy. In people with weakened immune systems, such as those with autoimmune diseases, those receiving chemotherapy, or organ transplant recipients, IgG antibodies may be present but not function as effectively, leaving them at risk for reactivation.

Testing for VZV IgG is clinically useful. A simple blood test can show whether someone has immunity. This is particularly important for adults who never had chickenpox or the vaccine, for women of childbearing age who risk severe illness during pregnancy, and for people with suppressed immunity. In populations without routine vaccination, most adults will test positive, but a significant minority may remain susceptible.

VZV IgG targets viral proteins on the virus’s surface, especially glycoprotein E. This same protein is the basis of Shingrix, the highly effective shingles vaccine. While IgG prevents primary infection, cellular immunity is essential to control reactivation, meaning both arms of the immune system must work together for lasting protection.

In short, the presence of VZV IgG antibodies signals past exposure and some degree of protection. Their measurement helps guide vaccination decisions, assess risk in vulnerable groups, and inform clinical care around pregnancy, immunosuppression, and shingles prevention.