Chickenpox (Varicella) is a highly contagious viral illness caused by the Varicella-Zoster Virus (VZV), a member of the herpesvirus family. The infection typically results in a characteristic itchy rash that progresses from small, red bumps to fluid-filled blisters that eventually crust over. Widespread vaccination has dramatically reduced the incidence of childhood cases, making the status of never having been infected a common and medically important consideration for adolescents and adults today.
How the Virus Spreads and Who Is At Risk
The Varicella-Zoster Virus is exceptionally contagious and spreads primarily through the air when an infected person coughs or sneezes. Direct contact with the fluid from the skin blisters can also transmit the infection. The virus is communicable starting one to two days before the rash appears and until all the lesions have crusted over.
The population considered “at risk” includes anyone who has neither had a documented case of chickenpox nor completed the full two-dose vaccination series. If immunity status is unsure, a simple blood test can check for the presence of VZV antibodies. This testing helps establish susceptibility, particularly for those in high-risk professions or women planning a pregnancy. Knowing one’s immunity is an important step in preventative care, as the virus almost always produces clinical disease upon exposure.
Potential Complications of Adult Infection
Contracting Varicella as an adolescent or adult often results in a far more severe and systemic illness compared to the milder cases seen in young children. The adult immune response, which is often delayed, can lead to extensive organ system involvement and greater morbidity. The most common serious complication is Varicella pneumonia, a viral infection of the lungs. While rare in healthy children, this complication is a significant concern for adults, carrying a risk of mortality and reported rates ranging from less than 5% to over 50% in some populations.
The infection can also lead to neurological complications, such as encephalitis (inflammation of the brain) or cerebellar ataxia (affecting balance and coordination). While these events are rare, occurring in approximately one to two cases per thousand, they can be life-threatening or result in long-term damage. Furthermore, the rash can lead to severe secondary bacterial infections of the skin, such as cellulitis, if blisters are scratched or improperly cared for. Primary Varicella infection in a non-immune adult is a serious medical event that often requires hospitalization.
Non-immune pregnant individuals face distinct and serious risks if they contract the virus. Infection during the first half of pregnancy, particularly the first 28 weeks, risks congenital varicella syndrome, which causes severe birth defects in the fetus. If the mother contracts the infection just before or immediately after delivery, the newborn is at high risk for developing severe, potentially fatal, neonatal varicella. The mother is also more susceptible to severe systemic illness, including Varicella pneumonia.
Gaining Protection Through Vaccination
The best defense against Varicella is the vaccine, which provides a safe and effective way to acquire immunity. Non-immune adolescents and adults require a two-dose series of the single-antigen Varicella vaccine, typically administered four to eight weeks apart. This complete two-dose regimen is highly effective, offering 92% to 98% protection against the disease and nearly 100% efficacy against severe cases.
Vaccination is recommended for non-immune adults in high-exposure settings, such as healthcare personnel, teachers, and non-pregnant women of childbearing age. If a susceptible person is exposed to the virus, post-exposure prophylaxis (PEP) can prevent or lessen the severity of infection. The Varicella vaccine, if administered within three days (and possibly up to five days) of exposure, can still provide protective benefits.
For high-risk individuals who cannot receive the live-virus vaccine (such as pregnant women or those who are severely immunocompromised), Varicella-Zoster Immune Globulin (VZIG) is the preferred post-exposure treatment. VZIG contains antibodies that offer immediate, temporary protection and must be given as soon as possible after exposure, ideally within 96 hours. Seeking prompt medical advice after exposure is crucial to determine the most appropriate preventative measure.