Elmo and President Barack Obama tell us to do it (see Elmo’s demonstration here), but is sneezing into our elbows effective at preventing the spread of germs?

With the start of school in New York City and elsewhere today and this week, reminders about “covering your cough” are rampant. That used to mean coughing into your hands, but for the past five years, the Centers for Disease Control and Prevention (and most doctors and educators) have been encouraging kids to cough and sneeze into their elbows.

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The reasoning makes sense: Kids touch a lot of things at school — over 300 surfaces in 30 minutes, according to GermyWormy — including their mouths, and most kids don’t run to the bathroom to wash their hands every time they cough or sneeze.

Some argue that attempting to sneeze into an elbow often fails and germs could be spread further. In fact, the CDC’s first recommendation seems to be the most failsafe: Cover your mouth and nose with a tissue when you cough or sneeze, and throw the tissue away.

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Most discouraging, perhaps, is the result of one of the only known studies on sneezing: Research during the 2009 swine flu pandemic found that only one in four people covered their sneezes at all.

“Probably the major transmission is from exposure to uncovered coughing, rather than contaminated surfaces,” Wilson told Reuters. “Public health people want the appropriate responses to be automatic” — that is, always cough into a tissue or your elbow.

Photo: CDC