> * In immediate prevaccine era, improved sanitation resulted in less frequent exposure and increased age of primary infection, resulting in large epidemics wit

> * In immediate prevaccine era, improved sanitation resulted in less frequent exposure and increased age of primary infection, resulting in large epidemics with high death count How do you suss out the difference between increasing sanitation vs vaccination in a time where sanitation is on an upwards trajectory? Polio is spread from feces. Eventually people stopped drinking contaminated water. full stop.