A, D - Incorrect: The auxiliary verb is creates a comparison between two entities that must be from the same type. In this case, one (virus) that is a type implies that the virus is simply a type. Or perhaps type may mean type of virus where of virus is understood.
B, C - Incorrect: The pronoun it does not have a clear antecedent. It can refer to virus or research facility. While it could be argued that it refers to virus, it is also clearly redundant in these two cases.
E - Correct: This answer fixes the comparison error by stating that the virus believed to be of a type and not is a type. The pronoun it has been removed.
E is a better answer choice than A, among other reasons, because E is a little more precise, and because E doesn’t insist that we understand that the word type actually means type of virus.