I think that the credibility of the passage, especially of the information given, is high, since it is being supported by the words delivered by a credible source, or an authority, on the matter (e.g Tom Frieden, Director of the CDC). Also, since what is being said, is more of an informational nature, explaining how the fight against the flu virus goes, and how difficult it is to stop it, it is enough to know that it has been said by an authority, a person who knows about the matter. However, this passage could also be enriched by adding a little bit of data, or further background information.
