The Varicella-Zoster Virus (VZV) causes chickenpox, a highly contagious disease primarily associated with a mild rash in childhood. For a notable portion of the adult population, particularly those born before the vaccine became widely available in 1995, uncertainty exists regarding their immunity status. While the vast majority of adults in the United States have immunity, either from natural infection or vaccination, a lack of protection against VZV presents a health concern. For someone who has never had chickenpox, exposure to the virus later in life can lead to a much more severe illness than the typical childhood case. Understanding one’s true immune status is the first step in mitigating the risks associated with contracting VZV as an adult.
Determining If You Are Truly Non-Immune
Relying on memory alone to determine immunity to chickenpox can be unreliable, as mild or subclinical infections often occur without a noticeable rash. Parents may not recall a very mild case, or the infection may have been so slight that it was dismissed as something else. For adults who are unsure of their history or lack vaccination records, a simple blood test offers the only definitive answer.
This test is known as a VZV antibody titer, which checks for the presence and concentration of Immunoglobulin G (IgG) antibodies against the virus. A positive result indicates that the immune system has previously encountered VZV, either through infection or vaccination, and is considered protected. A negative or equivocal result means that protective antibodies are absent or too low to be considered effective, confirming non-immune status. This laboratory confirmation is often required for healthcare workers, students, and women planning pregnancy.
Why Adult Chickenpox Is A Serious Concern
The primary VZV infection, chickenpox, is significantly more hazardous when contracted in adulthood compared to childhood. Adults face a substantially higher risk of severe complications and hospitalization, as the body’s immune response can be overly aggressive and damaging. Compared to children, healthy adults are estimated to be 25 times more likely to experience severe complications from the infection.
One of the most frequent and life-threatening complications is Varicella pneumonia, which affects up to 20% of adult cases requiring hospitalization. This condition, which involves inflammation of the lungs, typically presents with a dry cough and shortness of breath three to five days after the characteristic skin rash appears. Other serious outcomes include encephalitis (brain inflammation), bacterial superinfections of the skin lesions, and blood clotting issues.
Pregnant individuals who are non-immune face a unique and serious risk. Contracting chickenpox during the first 20 weeks of gestation can lead to Congenital Varicella Syndrome, which may cause severe birth defects in the fetus. Exposure to VZV near the time of delivery also carries a high risk for the newborn, necessitating immediate consultation and possible treatment with passive immunization. Hospitalization is much more likely for adults with chickenpox, particularly those over the age of 18.
The Role of the Varicella Vaccine
For any adult confirmed to be non-immune, the Varicella vaccine is the primary and most effective way to establish protection against VZV infection. Adults require a two-dose series of the single-antigen vaccine, administered four to eight weeks apart, to achieve the highest level of immunity. This two-dose regimen is highly effective, preventing chickenpox in approximately 90% of recipients and nearly 100% of severe disease cases.
There are specific circumstances where the vaccine cannot be given, such as to pregnant women, who must wait until after delivery to be vaccinated. Individuals who are severely immunocompromised or have a history of a life-threatening allergic reaction to a vaccine component, like gelatin or neomycin, should also not receive the vaccine. In cases where a non-immune person has been recently exposed to the virus, Post-Exposure Prophylaxis (PEP) with the vaccine is recommended within three to five days of exposure. Even if the exposure does not result in infection, the vaccine will still provide future protection against the virus.
Understanding Shingles Without Prior Infection
Shingles, also known as Herpes Zoster, is a different manifestation of the same Varicella-Zoster Virus that causes chickenpox. Shingles occurs when the VZV, which remains dormant in the nerve ganglia after a primary infection, reactivates years later. If a person has never had chickenpox and has never been vaccinated, they cannot develop shingles through natural reactivation because the virus reservoir does not exist in their body.
The only way for a non-immune adult to become at risk for shingles is to first contract the VZV, either through a natural chickenpox infection or, rarely, from the live-attenuated vaccine. Once the primary infection has occurred, the virus establishes latency and carries the potential for future reactivation as shingles. Avoiding the primary infection through vaccination is the most effective way to prevent the later risk of shingles.