Presymptomatic poly‐GA vaccination reduces inclusions and largely prevents TDP‐43 mislocalization, neuroinflammation, neuroaxonal damage, and motor deficits in GA‐CFP mice suggesting vaccination is a promising prevention strategy in the long prodromal phase of C9orf72 ALS/FTD. This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.