Invading Aliens, Weaponized Diseases, Supernatural Abilities, ect…
How do you make things that never happened plausible?
Less is More ~ Robert Browning
Luckily, not everyone is looking for alien biology or expecting an innocent civilian to understand why everyone is dying of the smallpox.
Just write what you have. I’m sure you have an idea or concept in your mind. Don’t worry about the holes in the detail. With an ignorant protagonist it can easily work.
Now what if your protagonist isn’t ignorant? He was the one who created the experiment or is the biologist assigned to study alien anatomy.
This is where the Internet becomes your best friend. You can research how to contain a virus or how long can you keep liquid in a contained space over the air.
The best thing about fiction though, you can make it up. With enough research and effort you can make any theory plausible.
You can say Super Human gained his powers from a foreign liquid discovered on Mars after it’s been spun at 120 kph after it was mixed with hydrogen and potassium. In turn created a unique chemical reaction that allowed Super Human’s cells to evolve.
You have the control. You have the power to make your story any way you want.
Remember don’t stress about the little issues until your revision stage.