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Several large observational studies have linked herpes zoster (shingles) vaccination to lower risk for developing dementia (for both the original live-attenuated vaccine and the later recombinant vaccine); however, confounding factors might have played heavily in those conclusions. To minimize confounding, an international team took advantage of a natural experiment: When the first shingles vaccine was introduced in Wales on September 1, 2013, its use was prohibited permanently in people older than 80 (specifically, people born before September 1, 1933), because of poor efficacy in older people.
Using a healthcare database that included most Welsh citizens, the researchers were able to identify people who were born just after September 1, 19…