Hi Richard. In case it's helpful but you missed the response, I posted this just now:
I suspect the paper is this one:https://childrenshealthdefense.org/defender/scientist-warning-covid-vaccines-parkinson-neurodegenerative-disorders/
Here's the deal about that organisation:https://en.wikipedia.org/wiki/Children's_Health_Defense
It's basically a bunch of far-right conspiracy theorists associated with Donald Trump and QAnon. If your relative isn't a Trump fan, that might perhaps give him pause?