BelgFrNethPolioinc1921-53.jpg
Polio incidence (case and death rates per 100,000) in Belgium, France and Netherlands, 1921-1953
(Matthieu-Jean Freyche and Johannes Nielsen, "Incidence of Poliomyelitis Since 1920," in Poliomyelitis (Geneva: World Health Organization), p. 71)
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