As you might guess, the infection played out like a short war. The immune system's T-cells took a while to respond (about 5 days after initial infection), but they were merciless when they arrived, slowing down by the 7th day and methodically killing off infected cells. They even stayed around for a few days in a heightened state to keep watch for any new threats. This was all expected, but rare to see in action.

The live study has already taught scientists some lessons. A lower virus dose doesn't automatically lead to fewer T-cells fighting back, for one thing -- viruses may affect an immune system's response, but they don't define it. You may see far larger results in the future, though. Real-time data could lead to more effective treatments for viruses, triggering swifter, stronger immune responses. You might not have to spend ages grappling with that flu or cough.