The hospital held a massive influenza drill at the campus Monday.
The goal is to get its nearly 7-thousand employees vaccinated by tomorrow night.
OSF's Emergency Response Team says in the wake of a crisis, it's important staff get their shots first.
This applies to all emergencies including H1N1 or an anthrax outbreak.
That way, if disaster strikes, an infected population can be taken care of.
"It's important to protect the healthcare workers," explained Disaster Preparedness Manager Troy Erbentraut. "Without the healthcare infrastructure we have nothing. So the team focuses on providing that medication to our internal staff members."
This is the first year for the medical drill.
Once flu season begins, staff members who are not vaccinated must wear a protective mask while at the hospital.