"However, Boeing mysteriously decided that the 787 should have engine free air con and pressure and cited efficiency as the reason. Really? When "efficiency" was the reason engine bleed air was used in the first place..... If it walks like a duck & quacks like a duck etc"
Unfortunately, the evidence simply doesn't seem to be there - and I have looked fairly thoroughly. A proper epidemiologist would doubtless do a better job, but the evidence seems to be all very anecdotal, rather than science based.
As for Boeing's decision not to use bleed-air, it really comes down to a policy decision. Since "Toxic cabin air" has become an accepted meme of "fake news" that no scientific findings can reverse, one simply has to accept it.
Boeing, quite sensibly, have concluded that because of this, they will no longer use bleed-air for pressurisation and accept the associated inefficiency. This will lead to somewhat higher fuel burns and all that that implies, but this can be offset by higher ticket prices and possibly reduced services to some destinations.
As so often in the "alternative fact" world we live in, the majority will be inconvenienced by the absolute refusal of a small number of people to take as truth various things that they want to believe, since the negative cannot be proven.