Flu vaccination linked to 40% reduced risk of Alzheimer’s disease

Dementia is preceded by many years of cognitive decline, it isn't something that just appears. A person with partially developed dementia that wouldn't get detected in a screen is still probably less likely to go get a flu shot, wouldn't you think?

exactly this, because there is no treatment diagnosis is delayed as long as possible to avoid the stigma, by the time people get a diagnosis they are generally at the point they forget when to feed themselves.

Prior to that the decline can be decades in the making. My gran obviously had dementia for 15 years before her diagnosis, by the time she was given it the only words she could say was "keep on keeping on"

It's certainly impressive that you thought up this profound and fundamental flaw in their study in just a few minutes pondering this on the couch and after briefly skimming a summary article published in a pop-media publication ... yet the fleet of scientists and researchers didn't consider this, factor it in, describe their control processes to cater for this and other confounding effects etc, for a study that spanned many years.

Refer my response to parent.

Specifically to your most recent point, however, I'd observe that if treatment diagnosis is delayed as long as possible to avoid the stigma, that would put back treatment diagnosis for both groups, so it's hardly a compelling distinction there.

Anyway, I'd expect people with dementia at the time of their flu shot would have been assessed by the caregiver, and they would probably have been taken to the clinic by a family or friend anyway.

The compelling anecdote of your gran notwithstanding, of course.

There is no diagnosis in the group that doesn't have dementia, there is no "after flu vaccine" in people who dont get the flu vaccine.

Its called selection bias.

The root cause of the measurement issue is that people are less likely to get the flu vaccine if they have dementia. People who had the flu vaccine are already much less likely to suffer cognitive decline even if the flu vaccine was a placebo.

This sort of stuff is why double blind RCTs exist and have millions spent on them.

Also why all the dementia treatments to date failed to work, because these issues are so often ignored.

Also perversely - mental assessments are typically carried out on people who doctors "dont" think have dementia (to rule it out as a cause of symptoms)

Consider this "back of the envelope" calculation. 10% of the population will develop dementia. having early dementia symptoms makes you 50% less likely to get the flu vaccine. 70% of people get the flu vaccine.

If you randomly selected 200 who didnt get the vaccine and 200 who did from this group, you would expect to see only 13 of the 200 develop dementia when vaccinated, but 53/200 in the unvaccinated group.

the online paper is here

https://content.iospress.com/articles/journal-of-alzheimers-...

They controlled by excluding patients if:

"they had a diagnosis of mild cognitive impairment (MCI), encephalopathy, or dementia of any cause during the look-back period, or if they filled a prescription for a medication indicated for AD"

Therefore they didnt exclude patients with early signs of cognitive impairment (because it is not possible to do so, because it is not recorded anywhere)

Right, so in an experiment to see who acquires AD through the decade the trial runs, they initially excluded people who may already have it. This seems a reasonable part of the method, given what they were looking for.

If your position continues to be that their numbers are skewed - and this is a HUGE correlation here - exclusively because people with dementia will forget to get a flu vaccination, then a) I think you are making unsupported claims, and b) you're arguing with the wrong person.

Perhaps throw the authors of the study a line and suggest this alternative hypothesis for the numbers they saw across their sample set of ~ 1 million people.

Thing is, like I said, it would be lovely.

But I also said, all they "proved" is that people who dont forget to get the flu vaccine are less likely to develop full blown dementia.

Just to bear that in mind if you think it brings us any closer to preventing/treating/curing dementia.