It was the perfect mix of ingredients for West Nile.

West Nile develops in stagnant water,

We're swapping what is working and what is not working.

The North American West Nile virus epidemic persists.

If [West Nile] goes that route, then it would be a situation where it's sort of oscillating. Every few years we'd have an outbreak or some cases and then maybe not much activity between years.

There were 284 deaths from West Nile virus last year, (but) 30,000 deaths from pneumonia and influenza, and those are diseases that we can immunize against, ... So this is still a quite rare condition and not something that people should be overly concerned about.