Why do some vaccines not work well in certain contexts?

Rotavirus vaccine is very effective in preventing this diarrhea inducing stomach illness in children in developed countries. But it appears that in certain poorer regions, i.e. Bangladesh, the same vaccine has a reduced effect, inducing sufficient immunity in fewer than half of the children who receive it. In the early days of the polio vaccine, a similar pattern was observed.

Why is this? What can be done about it? What does it all mean?

We interviewed Carina Storrs -- who visited the affected areas and has been writing about it over recent weeks -- here, at Ikonokast. Carina is a scientist-turned-science-journalist, and has done some excellent reporting on rotavirus vaccine. Have a listen.