NARVIK

NARVIK is a virus developed by Hiroshi Hatake at Arctic BioSystems. It comes in three forms:

Narvik-A is a virus constructed to alter the DNA of the recipient, for an as of yet unknown end-goal. So far, all subjects infected die as a result.
 * NARVIK-A has a projected 100% mortality rate.

Narvik-B is another attempt at the Narvik strain that alters the DNA of the recipient [without killing them]. Initial results show victims infected with the B strain have their consciousness overtaken by primal instincts, and have an urge to infect others through forced mouth-to-mouth contact - these victims are called Vectors. Other bodily fluids can also infect the target.
 * NARVIK-B has a 100% infection rate and 0% mortality rate.

Collective behaviour is not unlike a pack of wolves, in that there is a dominant member of the collective, and they hunt as a group. With high agility and strength, they are able to traverse deadly terrain with preternatural effectiveness.

Vectors have a unique type of vision that allows them to detect whether a person is a 'fellow' Narvik infectee, or is one of the Immortals - if the latter, they immediately become passive and subservient in behaviour until they have retreated a safe distance.

Cryogenically freezing a victim infected with Narvik-B slows the rate of the infection, allowing more time to pass before behaviour becomes aggressive and dangerous to others, and has also been proven to be required in administering the anti-viral cure.

Narvik-C is a third attempt at the Narvik strain that is self replicating and very deadly, advertised as being able to kill off 75% of the mortal human population. It is later revealed that Narvik-C was a lie aimed toward Julia Walker so she would arrive on the island of St. Germain to collect Mother which would sterilize the human population.
 * NARVIK-C has a unknown infection rate and unknown mortality ate.