marginally statistically significantP < .0001
On the contrary, vaccination against influenza was not associated with a decrease in the risk of Alzheimer’s disease in four studies [ 22 , 29 , 30 , 38 ] including 1 711 800 vaccinated and 8 197 135 controls, whilst a significant decrease in other forms of dementia was reported in three studies [ 28 , 30 , 38 ] (RR = 0.83; 95% CI 0.69–0.99; P = .049), even if marginally statistically significant, and for vascular dementia (RR = 0.59; 95% CI 0.47–0.75; P < .0001; I 2 = 0%).