Beyond Shingles: The Surprising Potential of the Shingles Vaccine

A synthesis of recent research indicates that the recombinant shingles vaccine (Shingrix) is associated with potential health benefits beyond its primary function of preventing herpes zoster infection. Multiple observational studies suggest links between vaccination and a reduced risk of dementia, as well as slower biological aging in older adults. While these findings show correlations, researchers state that further investigation is needed to confirm causality and understand the underlying mechanisms.

Overview of Shingles

Shingles, scientifically known as herpes zoster, is caused by the reactivation of the varicella-zoster virus, the same virus responsible for chickenpox. After an initial chickenpox infection, the virus remains dormant in the dorsal root ganglion, a cluster of neurons near the spinal cord. It can reactivate later in life, typically after age 50, traveling along nerve pathways to the skin.

Approximately one in three people in the United States experience shingles in their lifetime. The condition is characterized by a painful rash, often described as a stripe of blisters on one side of the body. Early symptoms may include a tingling sensation, skin sensitivity, itching, burning, and intense pain. Some individuals may also experience fever, headache, and fatigue.

Transmission

The virus can spread through direct contact with fluid in the blisters or by inhaling virus particles released from blisters. An individual is infectious from the time blisters appear until they are dry and scabbed, a process that typically takes seven to ten days. Blisters generally clear within two to four weeks. Individuals who have never had chickenpox would contract chickenpox upon exposure to the virus, not shingles.

Complications

Approximately 1% to 4% of individuals with shingles are hospitalized for complications. The Centers for Disease Control and Prevention (CDC) reports fewer than 100 annual shingles-related deaths in the US. Some individuals experience post-herpetic neuralgia (PHN), persistent nerve pain following a shingles outbreak, which can last for months or years. An estimated 10% to 18% of shingles patients develop PHN, with risk increasing with age. Other potential serious side effects include pneumonia, encephalitis, and hearing or vision loss.

Vaccine Efficacy and Uptake

The shingles vaccine available in the US and UK is called Shingrix. The CDC states that Shingrix is over 90% effective in preventing shingles in adults aged 50 and older with healthy immune systems. If a vaccinated individual contracts shingles, the vaccine can reduce the disease's severity. Vaccination also reduces the risk of severe complications, including PHN.

Recommendations

The CDC recommends two doses of Shingrix for adults aged 50 and older, administered two to six months apart. The agency also recommends vaccination for adults aged 19 and older with weakened immune systems, who can receive the second dose one to two months after the first. Booster doses are not currently recommended. Contraindications include current shingles infection, pregnancy, or a history of allergic reaction to Shingrix.

Uptake Statistics

Despite the prevalence of shingles, vaccination rates remain low. As of 2022, approximately 36% of adults over 50 had received at least one shingles vaccine dose. Among US adults aged 60 and older, 43.8% had received at least one dose. A study of nursing facility patients found that less than 2% had received Shingrix. Vaccination rates were lower for Black and Hispanic adults compared to white adults. Shingrix is typically covered by Medicare Part D, Medicaid, and commercial insurance.

Side Effects

The CDC reports no serious side effects associated with Shingrix. Temporary side effects may occur, including pain and swelling at the injection site, typically resolving within a day. Flu-like symptoms, such as a low-grade fever and aches, are also possible and may last for a few days. These side effects are generally more common after the first dose and in younger adults.

Association with Reduced Dementia Risk

"The level of protection observed was surprising." — Lead author Kaley Hayes

A study published June 16 in the Annals of Internal Medicine found that nursing home residents who received at least one dose of the shingles vaccine within a year of admission had a 5.8% lower risk of developing dementia over four years. The study analyzed health records of over 509,000 people aged 66 and older admitted to US nursing facilities from 2017 to 2022.

Comparative Studies

• Wales (2024, Nature): Found a 3.5% reduced dementia risk over seven years.
• Australia (2024, JAMA): Found a 1.8% reduced risk over 7.4 years.
• Canada (2024, Lancet Neurology): Found a 2% reduced risk over 5.5 years.

Demographic Differences

Hayes' study showed weaker dementia risk reduction among men and those who had previously received the older Zostavax vaccine. A study in Wales also found stronger protection in women. Researchers stated that sex differences in vaccine response and dementia pathology may contribute to these findings.

Potential Mechanisms

• Dr. Timothy Chang (UCLA) theorized that shingles virus reactivation may trigger amyloid and tau accumulation in the brain, and the vaccine may reduce neuroinflammation by boosting overall immunity.
• Dr. Jennifer Pauldurai (Inova) stated that the vaccine prevents shingles, which can stress the brain and worsen underlying dementia risks.
• Kaley Hayes noted that shingles is linked to increased heart disease and stroke risk, which may affect cognition.

Study Limitations

Ann Philbrick (University of Minnesota) noted that people who get vaccines may be more health-conscious, which could bias results. Hayes' study, however, was designed to mimic a randomized trial. Studies in Canada and Australia avoided bias by examining vaccine eligibility based on birth date rather than actual vaccination.

Association with Slower Biological Aging

Researchers Jung Ki Kim and Eileen Crimmins from the University of Southern California conducted a study on over 3,800 US participants aged 70 or older. The study, published in the Journals of Gerontology, examined the association between shingles vaccination and biological aging.

Key Findings

• Participants who received the shingles vaccine after age 60 performed better on composite measures of biological aging compared to unvaccinated individuals.
• Vaccinated individuals exhibited biological markers linked to lower inflammation and slower "molecular and overall biological aging."
• These associations remained consistent after accounting for demographic and health differences between the groups.

"Slowing biological aging could extend not just overall lifespan but also the years of 'healthy life.'" — Eileen Crimmins

Biological age, distinct from chronological age, refers to the health and functional age of a person's body at a molecular level.

Potential Mechanisms

Kim proposed that the vaccination might support healthier aging by mitigating inflammation and decreasing virus reactivation. The study highlighted the role of chronic inflammation, termed "inflammaging," in age-related conditions like heart disease and cognitive decline. Researchers noted that the precise underlying mechanisms remain unclear and require further investigation.

Additional Health Considerations

Beyond preventing shingles, emerging research suggests the shingles vaccine is associated with potential protection against dementia, as well as a slowing of biological aging. Studies have also indicated a potential link between shingles vaccination and reduced risk of stroke and heart attack. Researchers stated that while not a substitute for healthy habits, shingles vaccination may be one way to support broader health outcomes in older adults.

Future Research

The first version of the shingles vaccine received US licensing in 2006, and the newer recombinant vaccine (Shingrix) is now available. Researchers noted that future long-term studies are needed to fully ascertain the extensive health implications of the shingles vaccine, including its potential effects on dementia prevention and biological aging.