Varicella, commonly known as chickenpox, is a highly contagious disease caused by the Varicella-Zoster Virus (VZV). While typically a mild illness in childhood, VZV infection in non-immune adolescents and adults can lead to more severe complications like pneumonia or encephalitis. To determine whether a person has protective immunity against VZV, a blood test called a varicella titer is used. This test measures the concentration of Immunoglobulin G (IgG) antibodies, which are proteins the immune system creates in response to a past infection or vaccination. Knowing your immunity status is important for personal health and for preventing transmission to vulnerable populations.
Purpose of Varicella Titer Screening
Screening for varicella antibodies confirms protective immunity. A positive titer result means the body has sufficient IgG antibodies, indicating immunity from either a previous case of chickenpox or successful vaccination. If an adult who is not immune contracts VZV, the illness tends to be more severe, potentially involving serious complications such as bloodstream infections or inflammation of the brain.
The screening also plays a role in public health by identifying individuals who pose a transmission risk. Non-immune people can easily spread the virus to others who may be at risk for severe disease, including pregnant women and those with weakened immune systems. The titer test acts as an objective measure to verify the presence of long-term immune protection, which is important in settings where exposure or transmission could have serious consequences.
Who Requires Screening and Initial Testing Protocols
Initial varicella titer screening is highly recommended or mandated for specific groups who are at higher risk of exposure or who work with vulnerable populations. These groups often include healthcare personnel (HCP), military recruits, and students entering post-secondary institutions. Women who are planning a pregnancy or who are already pregnant are also often screened, as VZV infection during pregnancy can pose a risk to the fetus.
For most adults, the initial screening is often the only one needed if the result confirms immunity. Individuals born in the United States before 1980 are generally presumed to be immune due to widespread disease circulation, though this presumption is not applied to HCP or pregnant women, who require documentation or a positive titer. If a person has documented evidence of two doses of the varicella vaccine, a titer test is generally not recommended, as the vaccine record itself serves as proof of immunity.
If a person lacks documented evidence of vaccination or prior infection, a titer test is necessary to establish their immune status. The goal of this initial testing is to determine if vaccination is needed. For those confirmed to be immune, retesting is not typically required, as VZV immunity is generally considered long-lasting.
Understanding Results and Follow-Up Actions
A varicella titer test will typically yield one of three results: Positive, Negative, or Equivocal. A positive result indicates that a protective level of IgG antibodies is present, meaning the person is considered immune and requires no further action. A negative result means no detectable antibodies were found, and the person is susceptible to infection.
An equivocal result is uncertain, suggesting that some antibodies are present, but the level is too low to guarantee protection. Both negative and equivocal results require the same follow-up action: the individual should receive the two-dose varicella vaccination series. The doses are typically administered at least four to eight weeks apart for adults.
Retesting is only recommended after an individual receives the vaccine series following a negative or equivocal initial result. A post-vaccination titer is often drawn approximately six to eight weeks after the final dose to confirm that the person has successfully seroconverted. Once a positive titer result is achieved following this protocol, no further routine retesting is needed.