As a practical matter, studies about links between major diseases will always always be talking about correlation.
To reach 'causation' would require intentionally giving your experimental subjects Covid-19 (and in a way that didn't result in them knowing they'd had it!), and that's unlikely to pass muster with the ethics review board.
To reach 'causation' would require intentionally giving your experimental subjects Covid-19 (and in a way that didn't result in them knowing they'd had it!), and that's unlikely to pass muster with the ethics review board.