From the Guidelines
To prove if someone contracted chickenpox in the past, the most reliable method is a blood test called the varicella-zoster virus (VZV) antibody test, which detects the presence of IgG antibodies to the chickenpox virus, as recommended by the Advisory Committee on Immunization Practices (ACIP) 1. This test requires a simple blood draw, with results typically available within a few days, and the presence of these antibodies confirms past infection. Some key points to consider when interpreting the results of this test include:
- The sensitivity and specificity of the test, with some studies suggesting that latex agglutination (LA) tests may be more sensitive than commercial ELISAs 1
- The potential for false-positive results, particularly when using LA tests 1
- The importance of confirming the results with a detailed medical history and physical examination, if necessary
Alternatively, a detailed medical history may provide evidence if the person recalls having chickenpox or if medical records document the illness. Physical examination might reveal characteristic chickenpox scars, though not everyone develops permanent scarring. Testing is particularly important for adults with no clear history of infection who may be at risk for severe disease if infected later in life, or for pregnant women and immunocompromised individuals who need to know their immunity status. The antibody test works because the immune system produces specific antibodies when exposed to chickenpox, creating a lasting immunological memory that protects against future infections. Other methods of determining immunity, such as verification of a history of varicella disease or herpes zoster by a healthcare provider, may also be used 1. However, the VZV antibody test is generally considered the most reliable method for determining immunity to chickenpox. In health-care settings, serologic screening before vaccination of personnel without evidence of immunity is likely to be cost effective, as it can help prevent nosocomial transmission of the virus 1. Overall, the VZV antibody test is a valuable tool for determining immunity to chickenpox and can help prevent severe disease and complications in high-risk individuals.
From the Research
Proving Past Chickenpox Infection
To determine if someone has contracted chickenpox in the past, several methods can be employed:
- A history of previous varicella infection can provide a reliable marker for prior infection, especially for low-risk populations 2
- Serologic testing can be used to confirm immunity, particularly for those with a negative or uncertain history of varicella 2
- For populations at higher risk of varicella infection, such as healthcare workers or pregnant women, routine serum testing is recommended to verify immunity 2
Immunity and Vaccination
Varicella vaccination can generate immune responses that prevent natural infection for several decades 3
- Two doses of varicella vaccine administered in childhood have been effective in generating varicella-zoster virus (VZV) immune responses 3
- Immune responses developed during varicella can wane with increasing age or immune suppression, but protection can be restored with additional vaccination 3
Special Considerations
For high-risk individuals, such as immunocompromised people, preterm infants, and pregnant women, varicella zoster immune globulin (VARIZIG) can be administered as postexposure prophylaxis to prevent or attenuate varicella-zoster virus infection 4
- VARIZIG administration up to 10 days after varicella exposure has been associated with low rates of varicella in high-risk participants 4
- Understanding the immunological correlates of protection against varicella can help develop more effective strategies for prevention and treatment of severe varicella 5