Contagious
Part of speech: adjective
Definition: Of a disease, easily transmitted to others. Of a fashion, laughter, etc., easily passed on to others. Of a person, having a disease that can be transmitted to another person by touch.
Example sentence: Even if you're unhappy, just pretend that you're happy. Eventually, your smile will be contagious to yourself. I had to learn that. I used to think, 'I'm being fake,' but you know what? Better to be fake and happy than real and miserable.
Infectious
Part of speech: adjective
Definition: Transmitted from one person to another, usually through the air breathed.Able to infect others.Spreading quickly from one person to another.Memorable and invoking excitement or interest.
Example sentence: I have seen this happen in recent years with regard to pharmaceuticals and vaccines, where, working together, we are improving access to medicines and vaccines for infectious diseases in the poorest countries.