The way a virus enters the body really affects how it makes people sick. Here’s a simple breakdown of this idea:

1. Where Viruses Get In:

   • Some viruses, like the flu, usually come in through the nose and mouth. This means that about 30% to 50% of people who catch the flu are likely to feel its effects.
   • Other viruses, like norovirus, enter through our stomachs. When norovirus spreads, it can affect about 5% to 15% of people in a group.

2. How Our Bodies Fight Back:

   • When viruses enter through our mucous membranes (like in our nose and throat), our bodies can start to fight back right away. In fact, around 70% of the specific immune cells called T-cells are activated when the virus attacks these areas.

3. How Viruses Spread in the Body:

   • Some viruses, like HIV, can get into the bloodstream. When this happens, about 90% of patients will have the virus spreading in their bodies within just a few weeks.

Understanding how viruses get into our bodies can help us figure out how to prevent and treat infections.