“…Paper for PAA annual meeting, Austin, Texas, April 2019 infection with poliovirus beyond the age when infants were protected by passively acquired maternal antibody is postulated to increase the risk of clinical disease. (Nathanson et al 1993, p.8) Some of the ideas that are part of the hygiene hypothesis were present in the polio literature before Nathanson's refinement, f.e., Sabin (1947), Van Riper (1947, Rivers (1948), Aycock and Meadors (1948), Paul (1952), Horstmann (1953, and Rhodes (1955). Earlier still, Collins (1946) and Melnick and Ledinko (1951) noted that in regions free of epidemic poliomyelitis, there was a steep acquisition by age of poliovirus-neutralizing antibodies, indicating high levels of exposure despite lack of outbreaks.…”