O712 - Poliomyelitis; a review of its natural history

One interesting quote:

"It can be postulated that, in regions where poliomyelitis is endemic and where epidemics do not exist or have but lately made their appearance (Japan), the native populations are immune as a result of early exposure to poliomyelitis virus. This is also reflected in the young age distribution of cases. As a possible mechanism for the production of this immunity, it has been observed that sanitary conditions are more primitive in endemic areas than in countries afflicted by epidemics; primitive sanitation would tend to promote constant general dissemination of virus leading to exposure at an early age and the development of active immunity. In countries where sanitation is good or improving, dissemination of virus is generally less, opportunities for immunization are proportionately decreased, and consequently there develops periodically a population ripe for epidemics.
"This hypothesis seems not unreasonable and deserves to be tested by investigations carried out in endemic regions with primitive sanitation for the purpose of determining: 1) the detectability of the virus in the population and environment, (2) the development of antibody in relation to age, and, 3) the number of different immunological types of virus and their relationship to strains isolated in countries where epidemics prevail."

Citation: Ward, R. Poliomyelitis; a review of its natural history. Pediatrics 1, 132–138 (1948).