Previous research based on health records suggests a link between the shingles vaccine and lower rates of dementia. These studies, however, suffered from a major source of bias: vaccinated people also tend to be more health conscious, meaning that the observed effects may have been due to more general healthy behaviors as opposed to the vaccine itself.
On September 1st, 2013, Wales launched a vaccination program in which anyone 79 years old on that date was eligible for the vaccine for one year. This unusual health policy allowed researchers to analyze the effects of the shingles vaccine without previous biases.
In the current study, researchers looked at health records for over 280,00 adults aged 71 to 88 years old who did not have dementia at the start of the vaccination program. They then focused their analysis on those closest to the eligibility threshold and compared those who turned 80 the week before and 80 the week after. Vaccine uptake increased from 0.01% among patients 1 week too old to be eligible to 47.2% among those a week younger.
Ultimately, the researchers found that adults who had received the shingles vaccine were 20% less likely to develop dementia than those left unvaccinated over a seven-year follow-up period. Further analysis found that the two groups were indistinguishable in all characteristics, including level of education, diagnosis of common conditions like diabetes, heart disease, and cancer, and likelihood of getting other vaccinations and preventative treatments.
The researchers noted that the effect was stronger in women than men, perhaps due to sex differences in immune response or how dementia develops. Further research, including health records from England, Australia, New Zealand, and Canada- countries with similar rollouts- yielded similar results.
Senior author of the study, Pascal Geldsetzer, MD, PhD, assistant professor of medicine at Stanford University, is currently seeking philanthropic funding for a large, randomized controlled trial to further examine the link.
Sources: Science Daily, Nature
