What Makes a Virus ‘Contagious’ or ‘Rare’?

Imagine viruses are like little party guests. Some know everyone and invite all their friends, making the party huge. Others don’t know anyone and just sit quietly in a corner. The more they spread to others, the contagious they become. If they only show up once in a while, they’re rare.

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Examples

A sneeze from a sick person spreads the flu to many people.
The common cold is contagious because it spreads through coughs and handshakes.
A rare virus might only infect one person in a whole town.

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Categories: Biology · virus,infection,epidemiology