Over 72 hours, 14 of 28 children at a daycare develop sudden-onset vomiting, watery diarrhea, and low-grade fever lasting 24–36 hours each. No respiratory symptoms, rash, or blood in stool are reported. After the first three cases, staff began applying 62% ethanol hand sanitizer after every diaper change and before food preparation, and wiped all surfaces with the same product. Despite consistent use over the next two days, seven additional children became ill. Stool PCR from five symptomatic children returns positive for norovirus. The infection control officer states that the choice of disinfectant — not staff compliance — is responsible for ongoing transmission.
Which of the following best explains why the alcohol-based protocol failed to halt transmission?