Scientists' path to usable Zika vaccine strewn with hurdles

The world is once again asking scientists and drugmakers to come up rapidly with a vaccine for a viral disease that, in the latest case, few people had heard of until a few weeks ago, and even fewer feared.

Making a shot to generate an immune response against Zika virus, which is sweeping through the Americas, shouldn't be too hard in theory. However, producing a safe, effective and deliverable product to protect women and girls who are at risk is not easy in practice.