I really hate having to miss out on things because I’m sick. Though I imagine I’m not alone on that one. So I starting looking at how things spread and thus how to avoid them. From that, I've focused on two insights: 

we can carry, and even pass on, a cold two weeks before showing symptoms, 

and that we typically spend a majority of our time with a select group of people. The main issue is that by the time you see your friend, they’ve already gotten a cold from someone in their own circle of friends. So even though it wasn't their intention, your friends' closest friends seem to be the ones who are getting you sick. 

We pretty much have our phones on us at all times, so why not use them as a way to catalog interactions and use that data to notify people before they get sick. As a way of identifying the people around you, your phone could use a range of things from NFC, Bluetooth, shared networks and location data. Honestly I think a combination would work best. All of this would take place in the background and wouldn't require additional effort from the user. The only real responsibility for them would be updating their wellness status. Say they did report feeling like garbage, a wave of 

notifications would be sent to their top interactions, and also to the top interactions of those top interactions. Thus enabling us to get out ahead of the cold.

The notifications being sent would provide suggestions for how to maintain a strong immune system. And if symptoms last longer than expected and it turns out to be something more serious than the common cold, the app would allow you to contact your preferred doctor.

Getting people to update their wellness status could be a pain point. One way around it would be prompting people to update their status when someone else was reported as being sick. Another option, at least within the Android version, would be to have notifications ask the user how they were feeling and provide a few options to choose from. With these quick responses being accessible within the notification, users wouldn’t even be required to launch the app to update their status.

After reaching a sustained user base, health and wellness products could be promoted within the notifications as a means of monetizing the app. Now as a way to solve a larger social issue, anonymized interaction data could be sent to the Center for Disease Control. Providing them with models on how something more serious might spread, and what can be done to keep it from happening.