Alright so not entirely sure the feasibility of this event, so take it and roll with it.
Essentially I want to suggest an event that still involves a degree of interaction with the living city (and I will be suggesting others like that in future too).
In Rockford hospital, the existing medical staff will be recalled to examine a mysterious biological material the military brought in, for something of a pre-event. They will interact with some of the military there, who will want them to take a look at the object for testing, but understand that this is a life-threatening illness they are trying to understand.
If they agree, they'll be escorting to a back room where they will hook the object up to some machine, it'll start to process, but something will go wrong.
The object will break, and alarms will start to go off. The military will evacuate from the hospital entirely, to the PD, where they will turn it into a military base, while, before the back room doors of the hospital will unlock.
The preliminary doctors will be in the room with a staff member (who will be in RP as a doctor also). Who will convince them they need to find someone to help.
When the doors unlock, the doctors will go out into the city, to ask random players for help. When they do so, they will cough (or some such effect), that will make it clear they have passed some kind of illness onto a person. People infected with this illness, including the doctors, will slowly reduce in health, losing speed, and eventually sight, before after a lengthy time, dying.
As soon as it is clear people are being infected, two recruitment events will start.
1: Doctors. You will be able to join the new event job: Biohazard Science team. - You will need to figure out the right combination of chemicals to create a cure, and once created, dispatch it to sick people, eventually curing the city.
2: Containment. You will be able to join a new event job: Biohazard Extermination team. - You will be screened for disease and prepped for the nuclear option: When the timer runs out, you will be deployed, to kill the infected, wherever and whomever they are.
This might be quite a large event, though I think there are sufficient tools to make some version of it possible. You may even want to expand certain elements of it.
I wanted this to be involved with the city at large, because I felt that a certain point into the spread of the disease, people would start to bunker up, either to prevent illness from getting them, or the military from removing them. I don't think this event has been suggested like this before, but there's lot I feel can be done with it.