It supposedly causes the taker to see flashes of light that aren't there.
		
		
	 
And possible brain damage.  The stuff may have prophylactic properties but I don't trust it.  My sister and her husband have been knackers since they started taking it.  They have been taking it for a couple of years now.  By knackers I mean very weird.  They both have said some very bizarre things.  They used to be scholarly and intelligent.  The husband has had some very strange autoimmune things pop up too.
I just keep myself well nourished and eat foods known to boost the immune system.  I do think the government blew the Covid stuff way out of proportion and they didn't manage it properly.