Don’t worry. I’m not contagious. I’m Maddie Sofia. And what Adam just said is nonsense. Hey! You’re contagious for a lot longer than you might think. To find out why, we have to go back to when Adam first got the flu. Most of the time, the flu is transmitted from person to person through virus-containing particles. Yep, that’ll do it. Twenty-four hours later, the virus has started to take over. It hijacks Adam’s cells and starts multiplying, building up an army. Adam feels fine, but he’s already contagious. By now, Adam’s immune response has caught on to the foreign invaders and started a counterattack. And that’s actually what gives you your symptoms. Adam’s fever is actually helping him out. At high temperatures, the flu virus actually doesn’t grow that well, and some immune cells work even better. By Sunday, Adam’s feeling like garbage. His nose fills up with snot. That mucus is good at trapping foreign invaders before they can infect other cells. At this point, Adam’s airways are pretty beat up, and he starts to cough and sneeze. That works out really well for the flu because it helps it spread to somebody else. While Adam takes the day off, warriors of his immune system seek out and destroy virus-infected cells. But Adam’s immune system can actually damage his internal organs if it goes unchecked. So — as the amount of virus drops in Adam, the immune system dials itself back. He might feel more alert. He can probably even breathe through one nostril. But, there’s still some virus lurking inside Adam when he decides to come back to work. And in 3…2….1… Tiny droplets that fly from his mouth can travel as far as 20 feet at speeds ranging from 25 to 50 mph. Sometimes, they can stay suspended for hours. And that’s bad, because some of those droplets can contain virus that could get you sick. Adam is still contagious. In fact, the CDC says you are contagious one day before you start feeling sick, and up to seven days after. You’re probably the most contagious here in the middle. If you’re a kid, elderly, or you have a weak immune system, you can be contagious for even longer. So Adam, why don’t you take another day? Actually, alcohol can suppress the immune response. Get out of my house! Hi everybody! I’m Maddie Sofia. And I’m Adam Cole. I work with science correspondent Joe Palca on a project called Joe’s Big Idea. If you want to check out videos about the scientific invention process, click here. Please subscribe to our channel. There will be lots more videos featuring Maddie in the coming months.