Definitely. Throughout the manga, it's clear that Yona's love for Hak grows and becomes an important aspect of the story. Their relationship develops in various ways that show her affection for him.
A common characteristic is the strong emphasis on their loyalty to each other. In these fanfics, Hak is always by Yona's side, protecting her no matter what. Yona also shows her trust in Hak.
I'm not sure specifically about Han Sang Woon's work on the novel influenza. There could be many aspects such as studying its origin, transmission patterns, or developing new ways to diagnose or treat it.
You can start by looking on popular fanfiction platforms like FanFiction.net and Archive of Our Own (AO3). These platforms usually have a wide variety of fanfictions, including those about Yona and Hak.
In a Hak x Yona pregnant fanfiction, the plot could revolve around the couple's journey through the pregnancy. Yona might be concerned about how her new role as a mother - to - be will affect her leadership. Hak, on the other hand, is determined to be the best father and protector. There could be a lot of emotional moments, like when they feel the baby's first kick. And perhaps there are some complications during the pregnancy that require them to seek help from a wise healer in a far - off land. Along the way, they also have to deal with political unrest in the kingdom that threatens the safety of their unborn child.
I'm not sure of a specific 'Hak x Yona pregnant fanfiction' off - hand. But you could try searching on popular fanfiction websites like Archive of Our Own. They usually have a wide range of fanfictions for various fandoms, and you might be able to find one that fits this scenario.
There's no evidence to suggest that Han Sang Woon has made any big findings regarding the novel influenza yet. It could be that his research is still in progress. He might be in the early stages of data collection or analysis, which are necessary steps before any significant discovery can be made.