What is the tone of this story? Reassuring or frightening? Does it lend an air of confidence or add to the fright factor?

The tone is often intensely frightening. These scientists are doing their best to contain viruses that could wipe out humanity. Although the heroics and know how of scientists are commendable, I always got the feeling that it won't be long before a virus gets away on us. What is more immediately frightening is our overuse of antibiotics which has rendered many of them useless or weak against viruses.