Alright let's talk plot and themes.
Just as coming up with a joke starts with the punchline if you want a story's plot to have a cathartic payoff you start at the outcome then work your way backwards, detailing the events that lead up to that outcome with the goal of contextualizing it in a way that makes it more meaningful/impactful.
From the prologue of the Harry Potter series it's already abundantly clear that the conclusion of Harry's story will be his confrontation with Voldemort and the outcome of that confrontation is pretty obvious. So the entire story from beginning to end is a buildup to that payoff, sure we know Harry will defeat Voldemort but what's at stake, why do we care about about this and what is it going to cost him? Throughout the series he makes friends and enemies, has adventures, romantic interests, the Weasleys practically become his new family.
He goes from being an unloved overworked orphan living in a cupboard under the stairs with little to no prospects to having a lot to live for, and as the series is coming to a finale we find out he's the final horcrux and it's implied that defeating Voldemort may necessarily come at the cost of his own life.
Now that's just the overall plot, within that plot there's a lot of subplots which contribute to the main plot but are not individually essential but they all contribute to the main plot and without that context the main plot wouldn't be as meaningful.
A better example for the relationship between the main plot and subplots is "Pirates of the Caribbean: At World's End", the main plot is that the growing power of the East India Trading Company is bringing the age of piracy as a lifestyle to an end. This affects all the characters but for the most part they're not concerned about it directly, it's not until the very end that the pirates are all united in a common cause. What unites them is the subplot around the heart of Davy Jones and how the conflict over his heart is the crux of the overall conflict, whoever commands the unstoppable Flying Dutchman effectively rules the seas.
Within the Davy Jones subplot practically every major character has their own personal subplot, Will Turner wants to save his father, Elizabeth Swann wants to be reunited with Will, Jack just wants to be a free man but Davy Jones has killed him once already and he knows that with the EITC ruling the seas he either gives up his life of piracy or it will inevitably happen again.
Then there's Davy Jones and Calypso, their personal relationship issues are the focal point upon which the entire plot revolves and there's a synergy of themes between the large scale main plot of Cutler Beckett trying to bring the world's oceans under his control, and Davy Jones the man who fell in love with the embodiment of the sea and imprisoned her when her fickle nature broke his heart.
They're both men trying to control the uncontrollable.
In the final battle Barbossa frees Calypso (who resurrected him) and while captaining the Black Pearl and in the midst of a battle he marries Will and Elizabeth, meanwhile Jack is battling Jones for control of his heart, and they're all being drawn down into the maelstrom's whirlpool. It's absolutely bonkers and all these subplots are reaching their payoff at more-or-less the same time and because everything over the last three movies has built up to this point it feels amazingly epic.
So give it a thought, what's the overall plot of this story, what is it about thematically and what subplots will you have and how do they contextualize the main plot and/or bring the focus of the main plot down to a more personal scale?
For example you mentioned political tensions with China, if this outbreak is taking place in a border region between the two countries or during an event that's politically sensitive, and neither country is either willing or able to adequately respond to the outbreak due to their inability to coordinate with the other, then the outbreak itself becomes the focal point of a breakdown of international diplomacy.
This in turn could be brought into sharper focus with there being a mix of Chinese and Indian people in the quarantine area who are distrustful of each other and in turn further sub-sub-plots with each of these people having their own personal reasons to be distrustful and/or different perspectives on the situation.
The movie "12 Angry Men" is about a jury trying to decide whether some guy is guilty of murder or not with only circumstantial evidence and the whole movie takes place in a single room with just those twelve characters. Nothing really happens the entire time they're just talk but what makes the movie interesting (definitely worth watching) is that each has his own personal perspective and motivations, e.g. one guy has tickets to a baseball game and wants to leave ASAP regardless of the decision. Each also has their own definition of justice and opinion on whether the law should err on the side of punishing the guilty at the risk of punishing people who are not, or on the side of ensuring the innocent are not punished even if sometimes the guilty go free.