What Triggers Shingles?

Varicella zoster is the virus that keeps on giving. The first exposure to varicella zoster virus (VZV) results in chickenpox, typically in young children. It then takes a deep dive into sensory nerve roots and enters a dormant stage that can last for decades. In one out of three people, the virus fires up again in adulthood as shingles. The question that remains largely unanswered despite research is what triggers VZV to reactivate into shingles?

According to the CDC, an individual’s risk for developing shingles (herpes zoster) increases as their VZV-specific immune cells, which have been holding the virus in check, decline in number and functionality. Aging is the strongest risk factor for this decline in immunity. Statistically, half of all shingles cases in the United States are diagnosed in people aged 50 or older, and the risk continues to rise exponentially with each additional decade of life. 

Several other consistent risk factors for shingles have also been identified. “Women appear to be at higher risk than men, whites appear to be at higher risk than other ethnicities, and people who are immunocompromised also have an elevated risk of shingles,” says Kathleen Dooling, MD, MPH, Medical Officer, Division of Viral Diseases at the CDC. The immunocompromised category includes people with cancer and HIV, transplant patients, and individuals who are taking immunosuppressive medications including steroids and chemotherapy.

A number of recent research studies have examined more potential triggers for shingles. They have focused on physical trauma, psychological stress, family history, sleep disturbance, depression, recent weight loss, smoking, tonsillectomy, diet, and exposure to pesticides or herbicides. However, none of the studies have shown conclusively that there is a connection between any of these factors and shingles.

The incidence of shingles has been gradually but steadily increasing among adults in the United States. Virtually everyone over the age of 40 who was born and raised prior to the introduction of the chickenpox (varicella) vaccine in 1995 has been exposed to and infected with VZV, putting them at risk for shingles. Their only option for avoiding shingles is one of two vaccines: Zostavax and Shingrix, both approved by the FDA for people aged 50 years and older.

The CDC’s Advisory Committee on Immunization Practices (ACIP) recently recommended the use of Shingrix over Zostavax, which it considers to be less effective in the prevention of shingles and related complications, including postherpetic neuralgia. The ACIP also recommended that adults who have already received Zostavax be revaccinated with Shingrix.  

While neither vaccine is recommended for immunocompromised individuals, Dooling noted that Shingrix and another investigational vaccine are currently in trials to test their safety and efficacy in that group.