I think you might be overestimating the amount of 'formal' evidence. Obviously anyone with any amount of common sense worked out that a physical barrier would p

I think you might be overestimating the amount of 'formal' evidence. Obviously anyone with any amount of common sense worked out that a physical barrier would probably be helpful, but there weren't really the kind of formal studies that the medical establishment pretends to need. Your opinion is, as far as I can tell, broadly accepted fact (ie several officials said as much).