The research base isn't really where the CDC people were told it is.
As was pointed out in the Artistic License entries, a base with underground levels couldn't be constructed on the open ice, and it ought to be non-stop nighttime at the date and latitude where the story's alleged to take place. It could, however, have been built in northern Canada or Alaska off-the-books, with the relevant officialdom being bribed or coerced by Constance's company to pretend it's outside their jurisdiction.They run the company. NARVIK-B is Blacklight
Derived from a 100% lethal manmade virus that is intended for genocide? The victims become zombies with Super-Strength, enhanced vision and Black Blood? And they can communicate wordlessly, like in a Hive Mind (that apparently one person can control)? A corporation that may have created this at the behest of the government? Sounds like Alex Mercer may be on the Arctic Biosystems payroll. Immortals are sterile, and the Inuit children were given to them to raise as substitutes.
Well, barring the children used as fodder for experiments. The Immortals are, well, Immortals
The Immortals finally realized they'd make out better if they stopped killing each other and banded together to rule the world.- That explains why Hatake took Hvit and Sutton's heads off. (of course the Immortal under Echelon station didn't think beheading was necessary.
Some Event created the Immortals
Upon being told that Sarah has silver eyes like him, Michael gets thoughtful and confused and says, "That's impossible. She wasn't there." Something very specific happened that turned 500 random people into deathless, silver-eyed abominations around the same time. This includes the few Immortal children we've seen; it's established that immortality is not hereditary, so the Scythe and Durand must have been there for the event. Most likely it happened in Europe, given the disproportionate number of European Immortals, and the fact that Illaria is based in Paris. This doesn't explain Hatake, however, but there may be a number of reasons that a 16th-Century Japanese man might find himself in France; possibly a merchant or foreign dignitary...