Both chickenpox (Varicella) and shingles (Herpes Zoster) are caused by the same organism: the Varicella-Zoster Virus (VZV). Chickenpox is the initial, widespread infection with VZV, usually occurring in childhood. Shingles is the localized re-emergence of that same virus many years later. Understanding this two-stage process is key to determining the risk of shingles without a prior history of chickenpox.
How the Chickenpox Virus Causes Shingles
Shingles is a disease arising from within the body, making the primary infection with VZV a necessary prerequisite. Following the initial bout of chickenpox, the Varicella-Zoster Virus establishes a lifelong presence within the nervous system. The virus particles travel along the sensory nerves and settle in the dorsal root ganglia, which are clusters of nerve cells near the spinal cord.
In this location, VZV enters a state of dormancy, where its DNA remains present but largely inactive for decades. This established presence, known as latency, is maintained by the body’s immune system.
Shingles occurs when this long-dormant virus reactivates, often due to a decline in VZV-specific immunity, which commonly happens with increasing age. Upon reactivation, the virus multiplies in the nerve cells and travels back down the nerve fibers to the skin, causing the characteristic painful rash and blisters. A person who has never been exposed to VZV cannot develop shingles because the virus is not present in their nervous system to reactivate.
The Possibility of Unnoticed Infection
Many adults who believe they have never had chickenpox may still harbor the virus, as VZV infection does not always result in a recognizable illness. The initial infection can be subclinical, producing very mild or entirely asymptomatic symptoms that go unnoticed. This is especially true for infections that occur in infancy or early childhood.
Research suggests that over 99% of Americans aged 40 and older have evidence of past VZV infection, regardless of whether they remember having chickenpox. These individuals still carry the latent virus in their nerve ganglia and are at risk for shingles later in life. A simple blood test, which measures VZV-specific antibodies, can confirm whether a person has been exposed to the virus.
Confirming VZV exposure through an antibody titer provides clarity for individuals uncertain about their history. If the test reveals antibodies, it confirms the virus is latent in the body and that shingles is a possibility. If no antibodies are detected, the person is susceptible to chickenpox if exposed, but they cannot develop shingles.
Current Shingles Prevention Options
For individuals confirmed to have had VZV exposure, the primary method of prevention is the shingles vaccine. The preferred vaccine, Shingrix, is a non-live, recombinant product designed to boost specific immunity against the dormant virus. It is a two-dose series, separated by two to six months, and is highly effective at preventing shingles and its complications, such as long-term nerve pain.
The vaccine is routinely recommended for all healthy adults aged 50 and older. It is also recommended for adults aged 19 and older who have a weakened immune system, as this group is at higher risk for VZV reactivation. It is not necessary to be screened for past chickenpox infection before receiving the shingles vaccine.
For those who have never had VZV exposure, the first line of defense is the chickenpox (Varicella) vaccine, which prevents the initial infection. By preventing the primary infection, the Varicella vaccine removes the possibility of the virus establishing latency in the nerve tissue, thereby preventing the future development of shingles.