Two years ago I went to Cuba on holiday. While I was on a group visit to a collective farm the resident nurse was asked about the main medical problems encountered locally. She said that one of their main concerns was the steady increase in childhood asthma. On further questioning it was apparent that the asthma trends in Cuba over the last few decades have been broadly similar to those in the UK.
One would think that the environments were quite different; especially that Cuba has very little road traffic pollution, because it has very little road traffic. Climate and diet are different. One thing that Cuba does have in common with the UK is a comprehensive public health service, including mass childhood vaccination.
I would be tempted to jump to the conclusion that Mrs Mathews has hit the nail on the head, but Tony Bosworth of Friends of the Earth points out on the same page that some kinds of air pollution are felt a long way from their source. So asthma in Cuba and the UK might both be caused by global pollution of some kind. However, the coincidence of the vaccination programmes deserves close study.