I think this reinforces the hypothesis tau buildup and Alzheimer development are linked as side-effects of fighting infectious diseases. One thing newborns and seniors share is vulnerability to infections. Newborns because lack of previous exposure to pathogens. Seniors because of immune system senescence. Perhaps tau help protect newborns while they still lack acquired immunity to most common pathogens, and is reactivated back in some people by old age, as a Hail Mary effort to contain new or reactivating pathogens rampaging in face of failing defenses. That would explain the likely protective effect some vaccines, like shingles, have against Alzheimer.