Why are pandemics so hard to stop? Often it’s because the disease moves faster than people can be tested for it. The Defense Department is helping to fund a new study to determine whether an under-the-skin biosensor can help trackers keep up – by detecting flu-like infections even before their symptoms begin to show. Its maker, Profusa, says the sensor is on track to try for FDA approval by early next year. If it wins FDA approval next year, the two-part sensor could help spot new infections weeks before symptoms begin to show.