Something doesn’t add up. They say that up to 2007, when the ban was enacted, there was a steady rise in childhood asthma of more than 2% per year. But according to this, the number of smokers since 2000 was slowly but steadily declining.
So one would expect that if there was a direct correlation between smoking and childhood asthma, the number of admissions would also drop or at least stay the same, not increase.
It could be that while the number of smokers declined, the number of times that at least one person in a public space was smoking stayed the same. That is to say, it used to be that the average public space would have 10 smokers. Then, as smoking declined, the average public space would have 5 smokers. fer the ban, the public space has no smokers. It’s possible that in terms of triggering asthma, the shift from 10 to 5 was meaningless, but the shift from 5 to 0 was meaningful.
If the question is about why the number of children with asthma was increasing from 2002 to 2007, it may have something to do with the Hygene Hypothesis:
Allergies (which include asthma) have been increasing in children in first-world countries for a while now. The suspicion is that it has something to do with the fact that children’s immune systems don’t get a workout like they used to do. Regardless of whether that’s true or not, it’s clear that allergies are increasing in children in first-world countries. So what’s happened in the U.K. is that asthma was increasing over the long term. The smoking ban has caused the amount of asthma to drop sufficiently to counteract this.
What the news story tells me is not that asthma incidence is dropping, but that admissions to hospitals because of severe asthma exacerbations are reduced, and that this welcome change is linked to a smoking ban.
Presumably one would want to see the statistics for adults as well before positing a link too seriously, particularly since a ban in public areas like workplaces and pubs would have reached adults much more than children.