The biggest issue is that a large complex urbanized society cannot function if many of the people who make it function are out sick at the same time.
So this is not just about police, military and firefighters or health care workers; think of the people who hourly monitor a city's power grid and water supply. Think of ambulance drivers and bus drivers and people who order and oversee food and medical supply distribution. Think of people who fill medical prescriptions. Think of garbage collectors. And so on.
We are a long way from the day that robots can fill all the critical functions that we take for granted. Until the day arrives, critically important employees with all kinds of illnesses get themselves to work no matter what. This happens every year during flu season. But if you add a new virus that can put people out of commission for more than a week during the flu season, this is a severe test of modern civilization.