Originally Posted by homealone

poor analogy, heavy water is non toxic at the levels possible by 'releasing into reservoirs', is itself not radioactive & naturally occurs in the human body.

http://en.wikipedia.org/wiki/Heavy_water

On the other hand a mutated virus would, I agree, be a problem - but that has been said about 'bird flu', arguably a much more lethal strain, and it hasn't happened yet?

I don't think anyone is denying the possibility of a potential 'killer flu virus', just that reacting to each potential candidate as if it were 'the one' is not realistic.

- the nearest to a pandemic 'killer virus' in living memory has been HIV, in my opinion.