inferno by Dan Brown
This book feels like it's been through a heavy-handed editor...
It should have ended with a massive die-off chronicled by Langdon and Sienna. I.e. end the book with a Plague Hell chapter, a Merciful Purgatory chapter 5 years later, and an Immanent Heaven chapter 20 years later.
Before that, we get the reveal that the "mad scientist" wasn't as mad as his disciples; they wanted to unleash the virus and let God sort everyone out, whereas he wanted to spare the H+ neurodiverse kids. When his disciples found out that an antiviral had been engineered, they rage against him and force his suicide. After which they infect themselves and start searching for the vaccine.
The only reason Sienna and Langdon survive is because the antiviral was embedded in Dante's deathmask, and in washing away the PPPPPPP they were innoculated. Which might not be a blessing in that they get to witness a fully global apocalypse.