Yawning

Laughter shared between people.

Because for a brief moment, individuals forget about their differences, stresses, financial difficulties, etc., and enjoy some humor. That behavior, in turn, improves moods and places smiles on people's faces, which results in infecting others with a spirit of lightheartedness. Lord knows, society could use more of this kind of contagion.😜😝😎✌🏻️

A smile 😊

I was gonna say love but it somehow seems cheesy and way too obvious. I too am going to go with yawning.

Laughter..
Cos it is...

Smile and laughter.

Respiratory allergies. *cough, cough*

Cold and flu?

Laughter. It just is. :)

Laughter

Fear probably, or an airborne virus.

Hate? Jealousy?

Cabin fever

Greed.

Probably hemmoroids, I don't know why, I'm not a doctor
I'm just glad I havn't caught them!

Not the most but negativity can be contagious and that is the worst.

Fly swatting?

Stupidity.. there's an epidemic.

Laziness , one lazy person on the crew rubs off on everyone else.

Disease..

Laughter, because it's just so much fun to get lost in some silly moment.

Stupidity. One conservative caught it and liberals were born.