[Emory University's Christine] Moe observed up to a 96 percent reduction in stomach flu cases after washing with soap and/or water, as compared to a 54 percent reduction after sanitizer use. ...
Why is this the case, if Purell effectively disables more frightening bugs, like herpes and HIV? These viruses are enclosed in an envelope that helps them infect host cells but also makes them more susceptible to the drying effects of alcohol. In contrast, stomach viruses and the cold virus, which are non-enveloped, are more alcohol-resistant. Dr. James Arbogast of GOJO Industries, the company that invented Purell, suggests that a sanitizer made of 70 percent alcohol might inactivate stomach viruses more effectively, but such high-concentration sanitizers aren’t in common use; the Purell in your college’s dining hall is eight percent lower in alcohol.
While research suggests that stomach viruses can survive hand sanitizer, it’s less clear whether alcohol-based gels fend off the flu or the common cold. The University of Virginia’s Dr. Ronald Turner found that sanitizer users and old-fashioned soap-and-water users are infected with the flu and cold at an equal rate. Based on these results, Turner believes that hand-to-hand and hand-to-object contact is unlikely to spread these illnesses, which may be more contagious via air.
--Michaela Panter, Yale Daily News, on Purell's inefficacy