UPDATE 1-Scientists' path to usable Zika vaccine strewn with hurdles
* More companies join Zika vaccine development race
* Safe shot for at-risk women and girls a big challenge
* Full regulatory approval of vaccine will take years
* Commercial opportunity for Zika vaccine uncertain (Adds comment from Japanese drugmaker Takeda)
By Kate Kelland and Ben Hirschler
LONDON, Feb 3 (Reuters) - 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.
For a start, scientists around the world know even less about Zika than they did about the Ebola virus that caused an unprecedented epidemic in West Africa last year.
Ebola, due to its deadly power, was the subject of bioterrorism research, giving at least a base for speeding up vaccine work. This time, the knowledge gap is more daunting. Continuación...