If kids born just before and after a vaccine eligibility cutoff get vaccinated at different times, scientists can compare them to see if getting the vaccine early helps prevent dementia later in life — like a real-life experiment without random assignment.

People born just before and just after September 2, 1933, were treated almost the same except one group got a shingles vaccine and the other didn’t—scientists used this tiny difference to see if getting the shingles shot helped reduce deaths from dementia.

Getting the shingles vaccine might help lower your risk of dementia, and this isn’t just because everyone born on the same day got other free health services too — because no other program in Wales used that exact birth date as a cutoff, so the link is likely real.

Getting the shingles vaccine might help lower your risk of dementia, and this isn’t just because people born on a certain date got other free health services too—because researchers checked, and no other health benefits jumped up for people born on that exact day.