"Over the weekend, relations were pummelled further when the US announced that it would cut $800m (£500m) worth of military aid as punishment for Pakistan's perceived lack of co-operation in the anti-terror fight." It might not be THE reason, but I guess there would be less than the [1]20 cases of polio that there are now in Pakistan if that $800m hadn't been cut.

[1] http://www.endpolio.com.pk/polio-cases-district-wise-2016