Chickenpox (varicella) and shingles (herpes zoster) are both caused by the Varicella-Zoster Virus (VZV). The initial VZV infection causes chickenpox, a highly contagious illness characterized by an itchy, blister-like rash. The virus then remains hidden within the body for decades. Understanding this connection is necessary to clarify the role of the varicella vaccine in preventing later disease.
How the Chickenpox Virus Causes Shingles
The development of shingles is a direct consequence of the body’s initial encounter with the Varicella-Zoster Virus. After a person recovers from chickenpox, the VZV does not leave the body completely. Instead, the virus retreats into the nervous system, a process known as latency.
The VZV travels to the sensory nerve ganglia, which are clusters of nerve cells located near the spinal cord and the base of the skull. Here, the viral genetic material remains dormant, or inactive, for many years without causing any symptoms. Shingles occurs when this latent virus reactivates.
Reactivation often happens when the body’s cell-mediated immunity to VZV weakens, typically due to increasing age or a compromised immune system. The reactivated virus travels along the nerve fibers to the skin, causing the characteristic painful, localized rash of shingles. The rash typically appears in a distinct band on one side of the body.
Shingles Risk After Receiving the Chickenpox Vaccine
The chickenpox vaccine, known as the varicella vaccine, introduces the VZV into the body in a controlled manner. This vaccine contains a live, attenuated, or weakened, form of the virus. The goal of using a live virus is to stimulate a robust immune response that provides protection without causing the full-blown disease.
Because the vaccine uses a live virus, it retains the ability to establish latency in the nervous system, just like the wild-type virus acquired through natural infection. This means that an individual who received the varicella vaccine can still develop shingles later in life. Shingles caused by the vaccine strain of VZV is known as vaccine-strain zoster.
The weakened nature of the vaccine strain significantly reduces its potential for reactivation. While shingles can occur in vaccinated individuals, the virus is much less likely to emerge from latency and cause disease compared to the naturally acquired virus. Cases of vaccine-strain zoster are generally milder and less likely to cause severe complications than cases following natural infection.
Comparing Shingles Incidence: Natural Infection Versus Vaccination
The risk of developing shingles is substantially lower for individuals who received the varicella vaccine compared to those who contracted chickenpox naturally. The vaccine provides a major public health benefit by preventing most cases of chickenpox and simultaneously reducing the future burden of shingles. Studies have consistently demonstrated this reduced risk across different age groups.
Research indicates that the rate of shingles is approximately 80% lower in healthy children who were vaccinated against chickenpox compared to their peers who had the natural infection. In one study focusing on vaccinated adults, the observed incidence of shingles was 1.00 case per 1,000 person-years. This rate is markedly lower than the historical rates observed in unvaccinated populations, which ranged from 2.15 to 4.05 cases per 1,000 person-years in similar age groups.
This difference occurs because the live, attenuated virus in the vaccine establishes a less robust latent infection than the wild-type virus. While the vaccine does not eliminate the possibility of shingles, it drastically lowers the probability of future VZV reactivation. The reduction in the incidence of shingles is a significant long-term benefit of childhood varicella vaccination programs.
Reducing Your Risk of Shingles Later in Life
For all adults, regardless of whether they had chickenpox or received the childhood varicella vaccine, the primary method of preventing shingles is the zoster vaccine. The current recommendation is for a two-dose series of the recombinant zoster vaccine. This vaccine is not the same as the chickenpox vaccine.
The zoster vaccine is recommended for all healthy adults aged 50 years and older. It is also advised for adults aged 19 years and older who are or will be immunocompromised due to disease or therapy. Unlike the childhood vaccine, the zoster vaccine is a non-live, recombinant vaccine designed to produce a strong immune response against VZV.
The purpose of this vaccine is to boost the existing immunity against the VZV that is already latent in the body. By strengthening the immune system’s defense, the vaccine helps the body suppress the virus and prevent it from reactivating. This action significantly reduces the risk of developing shingles and its associated long-term complication, postherpetic neuralgia.