A shy researcher in an isolated science station falls in love with the voice of his Russian counterpart, when he doesn’t hear from her for 24 hours he sets out across the tundra to find her.

I like the idea, I think everyone has already made good suggestions. There's definitely a way to trim the word count and still stress the situation, physical conflict and the emotional one too.

And I don't see how "shy" works as a relevant character flaw.? It seems extraneous to the dramatic situation.

A character flaw is relevant to the plot? and should only be included in a logline if it creates complications, if it threatens to defeat the protagonist from achieving the objective goal.? How will his being shy threaten to defeat his attempt to save her life?

I like it, but I would like a more credible explanation of how he could be the only one in the universe with the medicine. A bit far-fetched? Or make it clear how he is the only one having this medicine. What sort of illness is it and why would the cure only be in his hands.