The article is not credible for the reasons already stated so well above. Some additional points to keep in mind:
• The linked website is a blog masquerading as a news site. Why would they need to fake their credentials if the truth were on their side?
• The article leads with a claim about documents released by the UK, but never links to them (or else buries them so thoroughly they are impossible to find). Why would they neglect to provide the key evidence for their claim?
• Instead of providing the documents, the article links to various other sites making the same or related claims. This makes it look like the story is well documented, but in fact these links add little to the conversation. Why fake documentation if there is real evidence available?
• The main argument presented by the article is fallacious. In lieu of the supposed revelatory documents, readers are presented with the fact that the CDC has not answered a similar FOIA claim. This refusal is taken as evidence that the CDC is hiding something (which is the same “if you have nothing to hide” rationale used to justify the NSA spying program). But using the CDC’s actions as proof of wrongdoing is an argument from ignorance fallacy. Just because the CDC has not bothered to respond to some crackpot doesn’t mean the crackpot is right. I don’t engage the guy downtown who claims space aliens are stealing my organs at night, but that doesn’t mean I should guard my spleen more closely. Why argue fallaciously if there’s a good argument available?